Encoder, a decoder and corresponding methods of signaling and semantics in parameter sets

ABSTRACT

Signalling of syntax elements in a sequence parameter set of a video bitstream is addressed. Particularly, it is provided a method of decoding a video bitstream wherein a sequence parameter set, SPS, is coded that contains syntax elements that apply to a video sequence, the method comprising obtaining a value of a first syntax element from the SPS used to specify whether a decoded picture buffer, DPB, parameters syntax structure is present in the SPS and obtaining a value of a second syntax element from the SPS, at least when determining that the value of the first syntax element specifies that the DPB parameters syntax structure is present in the SPS, used to specify the presence of a DPB syntax element in the DPB parameters syntax structure, wherein the DPB syntax element is applied to a temporal sublayer except for the highest temporal sublayer in the video sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2021/078313, filed on Feb. 27, 2021, which claims priority toInternational Patent Application No. PCT/EP2020/055269, filed on Feb.28, 2020 and International Patent Application No. PCT/EP2020/065989,filed on Jun. 9, 2020 and International Patent Application No.PCT/EP2020/065999, filed on Jun. 9, 2020. All of the aforementionedpatent applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field ofpicture processing and more particularly to signalling of syntaxelements in a sequence parameter set.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

In particular, the signalling of syntax elements in the sequenceparameter set coded in a bitstream that are used for providing DecodedPicture Buffer information suffers from inefficiencies and eveninconsistencies in the art (see detailed description below). Thus, it isan object of the present application to provide techniques of signallingsuch syntax elements with an improved coding efficiency.

SUMMARY

Embodiments of the present application provide apparatuses and methodsfor encoding and decoding according to the independent claims.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further implementation forms are apparent fromthe dependent claims, the description and the figures.

According to a first aspect, the embodiment of the disclosure relates toa method of decoding a video bitstream implemented by a decoding device,wherein a sequence parameter set, SPS, is coded in the video bitstreamand contains syntax elements that apply to a video sequence. The methodcomprises obtaining a value of a first syntax element (for example, aflag) from the SPS, wherein the value of the first syntax element isused to specify whether a decoded picture buffer, DPB, parameters syntaxstructure is present in the SPS. The method further comprises obtaininga value of a second syntax element (for example, a flag) from the SPS,at least when determining (it is determined) that the value of the firstsyntax element specifies that the DPB parameters syntax structure ispresent in the SPS, wherein the value of the second syntax element isused to specify the presence of a DPB syntax element in the DPBparameters syntax structure, wherein the DPB syntax element is appliedto a temporal sublayer except for the highest temporal sublayer in thevideo sequence.

For example, the value of the second syntax structure may be onlyobtained, when it is determined that the value of the first syntaxelement that specifies that the DPB parameters syntax structure ispresent in the SPS. Here and in the following, the first syntax elementmay be sps_ptl_dpb_hrd_params_present_flag according to the detaileddescription below and the second syntax element may besps_sublayer_dpb_params_flag according to the detailed descriptionbelow. Here and in the following, the DPB syntax element may be one ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] according to the detailed descriptionbelow.

The, thus, provided method of decoding a video bitstream guaranteesefficient signalling of DPB syntax elements. Particularly, the secondsyntax element reliably controls the presence of the DPB syntax elementsof the DPB parameters syntax structure when the same is present.

According to an embodiment, the method further comprises obtaining avalue of the DPB syntax element based on the value of the second syntaxelement (for example, when the second syntax element specifies that theDPB syntax element is present in the DPB parameters syntax structure,particularly, only when the second syntax element specifies that the DPBsyntax element is present in the DPB parameters syntax structure) andreconstructing the video sequence based on the value of the DPB syntaxelement. The reconstruction of the video sequence can thus be achievedbased on a reliable and efficient signalling of the DPB information.

The operation of obtaining the value of the DPB syntax element based onthe value of the second syntax element may comprise:

obtaining the value of the DPB syntax element from the DPB parameterssyntax structure, when determining (it is determined) that the value ofthe second syntax element specifies that the DPB syntax element ispresent in the DPB parameters syntax structure or

setting the value of the DPB syntax element equal to a value of anotherDPB syntax element applied to the highest temporal sublayer in the DPBparameters syntax structure, when determining (it is determined) thatthe value of the second syntax element specifies that the DPB syntaxelement is not present in the DPB parameters syntax structure.

Thereby, it can be guaranteed that a definite value of the DPB syntaxelement is available in any situation and can be used for reconstructingthe video sequence and it is not to be worried about any indefinitebehavior in this respect.

The, thus, reliably obtained value of the DPB syntax element can be usedfor configuring the DPB, for example, for storing reference picturesused for inter prediction processing. Accordingly, the operation ofreconstructing the video sequence based on the value of the DPB syntaxelement may comprise configuring the DPB based on the value of the DPBsyntax element and reconstructing the video sequence using the DPB.

In an embodiment, the operation of reconstructing the video sequencebased on the value of the DPB syntax element may comprise reconstructingthe video sequence based on determining that the DPB used satisfies therequirement specified by the value of the DPB syntax element. Thus, itcan be checked whether a DPB provided is suitable for the reconstructionof the video sequence.

According to an embodiment, the method of decoding a video bitstreamfurther comprises

obtaining a value of a third syntax element from the SPS, wherein thevalue of the third syntax element is used to determine the maximumnumber of temporal sublayers that are present in the video sequence. Thevalue of the third syntax element may be zero, if there is only onetemporal sublayer. Determination of the maximum number of temporalsublayers that are present in the video sequence is facilitated bysimply signalling the third syntax element which may be advantageouswith respect to the coding efficiency.

Here and in the following the third syntax element may besps_max_sublayers_minus1 according to the detailed description below.

The operation of obtaining the value of the second syntax element fromthe SPS may comprise

determining whether the maximum number of the temporal sublayers in thevideo bitstream is greater than 1 based on the value of the third syntaxelement, when determining (it is determined) that the value of the firstsyntax element specifies that the DPB parameters syntax structure ispresent in the SPS and obtaining the value of the second syntax elementfrom the SPS, when determining (it is determined) that the maximumnumber of temporal sublayers is greater than one. For example, the valueof the second syntax element may be obtained from the SPS, only when itis determined that the maximum number of temporal sublayers is greaterthan one. Thereby, the coding efficiency may be further enhanced, sincein the case that the maximum number of temporal layers is not greaterthan one (i.e., there is only one temporal sublayer), the value of thesecond syntax element may not be read at all (for example, if it becomesmeaningless in this case) and for the single temporal layer DPB syntaxelements may be always signaled in the SPS.

According to a second aspect, it is provided a method of encoding avideo bitstream implemented by an encoding device, wherein a sequenceparameter set, SPS, is encoded in the video bitstream and containssyntax elements that apply to a video sequence, which shows the sameadvantages as discussed above. The method comprises the operations of:

determining the presence of a decoded picture buffer, DPB, parameterssyntax structure in the SPS;

encoding a value of a first syntax element (for example, a flag) intothe SPS based on the determining of the presence of the DPB parameterssyntax structure in the SPS, wherein the value of the first syntaxelement is used to specify whether the DPB parameters syntax structureis present in the SPS;

determining the presence of a DPB syntax element in the DPB parameterssyntax structure, when determining (it is determined, for example, onlywhen it is determined) that the DPB parameters syntax structure ispresent in the SPS, wherein the DPB syntax element is applied to atemporal sublayer except for the highest temporal sublayer in the videosequence; and

encoding a value of a second syntax element (for example, a flag) intothe SPS based on the determining of the presence of the DPB syntaxelement in the DPB parameters syntax structure, wherein the value of thesecond syntax element is used to specify the presence of the DPB syntaxelement in the DPB parameters syntax structure.

According to an embodiment, the encoding method further comprisesdetermining a value of the DPB syntax element when determining (it isdetermined) that the DPB syntax element is present in the DPB parameterssyntax structure; and reconstructing the video sequence based on thevalue of the DPB syntax element.

According to an embodiment, the encoding method further comprisessetting the value of the DPB syntax element equal to a value of anotherDPB syntax element applied to the highest temporal sublayer in the DPBparameters syntax structure and reconstructing the video sequence basedon the value of the DPB syntax element.

The operation of reconstructing the video sequence based on the value ofthe DPB syntax element may comprise configuring the DPB to satisfy thevalue of the DPB syntax element and reconstructing the video sequenceusing the DPB.

According to an embodiment, the presence of a DPB syntax element in theDPB parameters syntax structure is determined, when it is determined(for example, only when it is determined) that the DPB parameters syntaxstructure is present in the SPS and the maximum number of temporalsublayers in the video bitstream is greater than one.

Further, an apparatus for decoding and an apparatus for coding a videobitstream are provided which, respectively, show the same advantages asthe above-described methods.

According to a third aspect, it is provided an apparatus for decoding a(coded) video bitstream, wherein the apparatus comprises:

an obtaining unit configured to obtain a value of a first syntax element(for example, a flag) from the SPS, wherein the value of the firstsyntax element is used to specify whether a decoded picture buffer, DPB,parameters syntax structure is present in a SPS coded in the videobitstream; and

a determining unit configured to determine whether the value of thefirst syntax element specifies that the DPB parameters syntax structureis present in the SPS; and wherein

the obtaining unit is further configured to obtain a value of a secondsyntax element (for example, a flag) from the SPS, at least whendetermining (it is determined, for example, only when it is determined))that the value of the first syntax element specifies that the DPBparameters syntax structure is present in the SPS, wherein the value ofthe second syntax element is used to specify the presence of a DPBsyntax element in the DPB parameters syntax structure, wherein the DPBsyntax element is applied to a temporal sublayer except for the highesttemporal sublayer in the video sequence.

For example, the value of the second syntax structure may be onlyobtained by the obtaining unit, when it is determined that the value ofthe first syntax element that specifies that the DPB parameters syntaxstructure is present in the SPS.

According to an embodiment, the obtaining unit is further configured forobtaining a value of the DPB syntax element based on the value of thesecond syntax element and reconstructing the video sequence based on thevalue of the DPB syntax element.

Obtaining the value of the DPB syntax element based on the value of thesecond syntax element may comprise:

obtaining the value of the DPB syntax element from the DPB parameterssyntax structure, when determining (it is determined) that the value ofthe second syntax element specifies that the DPB syntax element ispresent in the DPB parameters syntax structure or

setting the value of the DPB syntax element equal to a value of anotherDPB syntax element applied to the highest temporal sublayer in the DPBparameters syntax structure, when determining (it is determined) thatthe value of the second syntax element specifies that the DPB syntaxelement is not present in the DPB parameters syntax structure.

Reconstructing the video sequence based on the value of the DPB syntaxelement may comprise configuring the DPB based on the value of the DPBsyntax element; and reconstructing the video sequence using the DPB.

Wherein DPB is used to store pictures for constructing reference picturelist.

In an embodiment, reconstructing the video sequence based on the valueof the DPB syntax element may comprise reconstructing the video sequencebased on the determining that the DPB used satisfies the requirementspecified by the value of the DPB syntax element.

According to an embodiment, the obtaining unit is further configured forobtaining a value of a third syntax element from the SPS, wherein thevalue of the third syntax element is used to determine the maximumnumber of temporal sublayers that are present in the video sequence.

Obtaining the value of the second syntax element from the SPS maycomprise

determining whether the maximum number of the temporal sublayers in thevideo bitstream is greater than 1 based on the value of the third syntaxelement, when determining (it is determined) that the value of the firstsyntax element specifies that the DPB parameters syntax structure ispresent in the SPS and obtaining the value of the second syntax elementfrom the SPS, when determining (it is determined) that the maximumnumber of temporal sublayers is greater than one.

According to a fourth aspect, it is provided an apparatus for encoding avideo bitstream, wherein the apparatus comprises:

a determining unit configured to determine the presence of a decodedpicture buffer, DPB, parameters syntax structure in a SPS;

an encoding unit configured to encode a value of a first syntax element(for example, a flag) into the SPS based on the determining of thepresence of the DPB parameters syntax structure in the SPS, wherein thevalue of the first syntax element is used to specify whether the DPBparameters syntax structure is present in the SPS; wherein

the determining unit is further configured to determine the presence ofa DPB syntax element in the DPB parameters syntax structure, whendetermining (it is determined, for example, only when it is determined)that the DPB parameters syntax structure is present in the SPS, whereinthe DPB syntax element is applied to a temporal sublayer except for thehighest temporal sublayer in the video sequence; and wherein

the encoding unit is further configured to encode a value of a secondsyntax element (for example, a flag) into the SPS based on thedetermining of the presence of the DPB syntax element in the DPBparameters syntax structure, wherein the value of the second syntaxelement is used to specify the presence of the DPB syntax element in theDPB parameters syntax structure.

According to an embodiment, the determining unit is further configuredfor determining a value of the DPB syntax element when determining (itis determined) that the DPB syntax element is present in the DPBparameters syntax structure; and reconstructing the video sequence basedon the value of the DPB syntax element.

According to an embodiment, the encoding unit is further configured forsetting the value of the DPB syntax element equal to a value of anotherDPB syntax element applied to the highest temporal sublayer in the DPBparameters syntax structure and reconstructing the video sequence basedon the value of the DPB syntax element.

Reconstructing the video sequence based on the value of the DPB syntaxelement may comprise configuring the DPB to satisfy the value of the DPBsyntax element; and reconstructing the video sequence using the DPB.

According to an embodiment, the determining unit is configured fordetermining that a DPB syntax element is present in the DPB parameterssyntax structure, when the determining unit determines that the DPBparameters syntax structure is present in the SPS and the maximum numberof temporal sublayers in the video bitstream is greater than one.

The above-described methods can be implemented in decoding or encodingdevices, respectively, Accordingly, it is provided an encoder comprisingprocessing circuitry for carrying out the method of encoding a videobitstream according to any one of the above-described examples. Further,it is provided an encoder comprising one or more processors and anon-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures theencoder to carry out the method of encoding a video bitstream accordingto any one of the above-described examples. Similarly, it is provided adecoder comprising processing circuitry for carrying out the method ofdecoding a video bitstream according to any one of the above-describedexamples and a decoder comprising one or more processors and anon-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures thedecoder to carry out the method of decoding a video bitstream accordingto any one of the above-described examples.

Furthermore, it is provided a computer program product comprising aprogram code for performing the method according to any one of theabove-described examples when executed on a computer or a processor.Similarly, it is provided a non-transitory computer-readable mediumcarrying a program code which, when executed by a computer device,causes the computer device to perform the method of any one of theabove-described examples.

Moreover, it is provided a non-transitory storage medium which includesan encoded bitstream, the bitstream being generated by dividing acurrent picture of a video signal or an image signal into a pluralityblocks, and comprising a plurality of syntax elements, wherein theplurality of syntax elements comprises a first syntax element in a SPS,wherein the value of the first syntax element is used to specify whethera decoded picture buffer, DPB, parameters syntax structure is present inthe SPS; in case that the value of the first syntax element specifiesthat the DPB parameters syntax structure is present in the SPS, thebitstream further comprises a second syntax element in the SPS, whereinthe value of the second syntax element is used to specify the presenceof a DPB syntax element in the DPB parameters syntax structure, whereinthe DPB syntax element is applied to a temporal sublayer except for thehighest temporal sublayer in the video sequence.

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the disclosure are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the disclosure;

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the disclosure;

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the disclosure;

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the disclosure;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 is an example of raster scan order;

FIG. 7 is an example of tiles, slices and subpictures;

FIG. 8 is a block diagram showing an example structure of a contentsupply system 3100 which realizes a content delivery service;

FIG. 9 is a block diagram showing a structure of an example of aterminal device;

FIG. 10 shows an example of picture partitioning;

FIG. 11 shows an example about layers and sub-lays of scalable videocoding;

FIG. 12 shows another example of picture partitioning;

FIG. 13 shows another example of picture partitioning.

FIG. 14 illustrates a method of decoding a video bitstream according toan embodiment.

FIG. 15 illustrates a method of encoding a video bitstream according toan embodiment.

FIG. 16 illustrates a method of decoding a video bitstream according toan embodiment.

FIG. 17 illustrates a method of encoding a video bitstream according toan embodiment.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the disclosure orspecific aspects in which embodiments of the present disclosure may beused. It is understood that embodiments of the disclosure may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present embodiment ofthe disclosure is defined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method operations are described, a correspondingdevice may include one or a plurality of units, e.g. functional units,to perform the described one or plurality of method operations (e.g. oneunit performing the one or plurality of operations, or a plurality ofunits each performing one or more of the plurality of operations), evenif such one or more units are not explicitly described or illustrated inthe figures. On the other hand, for example, if a specific apparatus isdescribed based on one or a plurality of units, e.g. functional units, acorresponding method may include one operation to perform thefunctionality of the one or plurality of units (e.g. one operationperforming the functionality of the one or plurality of units, or aplurality of operations each performing the functionality of one or moreof the plurality of units), even if such one or plurality of operationsare not explicitly described or illustrated in the figures. Further, itis understood that the features of the various exemplary embodimentsand/or aspects described herein may be combined with each other, unlessspecifically noted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g. by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g. by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g. by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions (e.g.intra- and inter predictions) and/or re-constructions for processing,i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3.

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g. a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g. to a destinationdevice 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e.optionally, comprise a picture source 16, a pre-processor (orpre-processing unit) 18, e.g. a picture pre-processor 18, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g. a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g. an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g. from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g. the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder30), and may additionally, i.e. optionally, comprise a communicationinterface or communication unit 28, a post-processor 32 (orpost-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g. directly from the source device 12 or from anyother source, e.g. a storage device, e.g. an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g. a direct wired or wireless connection,or via any kind of network, e.g. a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g. packets, and/orprocess the encoded picture data using any kind of transmission encodingor processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g. to send andreceive messages, e.g. to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g. the decoded picture 31, to obtain post-processedpicture data 33, e.g. a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g. color formatconversion (e.g. from YCbCr to RGB), color correction, trimming, orre-sampling, or any other processing, e.g. for preparing the decodedpicture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g. to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g. anintegrated or external display or monitor. The displays may, e.g.comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a videodecoder 30) or both encoder 20 and decoder 30 may be implemented viaprocessing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented via processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.The decoder 30 may be implemented via processing circuitry 46 to embodythe various modules as discussed with respect to decoder 30 of FIG. 3and/or any other decoder system or subsystem described herein. Theprocessing circuitry may be configured to perform the various operationsas discussed later. As shown in FIG. 5, if the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g. notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

For convenience of description, embodiments of the disclosure aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of thedisclosure are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2, the video encoder 20 comprises aninput 201 (or input interface 201), a residual calculation unit 204, atransform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, apicture 17 (or picture data 17), e.g. picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g. previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g. like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g. one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g. aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g. a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block, e.g. the encoding andprediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices (alsoreferred to as video slices), wherein a picture may be partitioned intoor encoded using one or more slices (typically non-overlapping), andeach slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using tile groups(also referred to as video tile groups) and/or tiles (also referred toas video tiles), wherein a picture may be partitioned into or encodedusing one or more tile groups (typically non-overlapping), and each tilegroup may comprise, e.g. one or more blocks (e.g. CTUs) or one or moretiles, wherein each tile, e.g. may be of rectangular shape and maycomprise one or more blocks (e.g. CTUs), e.g. complete or fractionalblocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g. by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g. a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g. by inversetransform processing unit 212 (and the corresponding inverse transform,e.g. by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g. bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g. a typeof transform or transforms, e.g. directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g. by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding and/or the inverse dequantization, e.g. byinverse quantization unit 210, may include multiplication by thequantization step size. Embodiments according to some standards, e.g.HEVC, may be configured to use a quantization parameter to determine thequantization step size. Generally, the quantization step size may becalculated based on a quantization parameter using a fixed pointapproximation of an equation including division. Additional scalingfactors may be introduced for quantization and dequantization to restorethe norm of the residual block, which might get modified because of thescaling used in the fixed point approximation of the equation forquantization step size and quantization parameter. In one exampleimplementation, the scaling of the inverse transform and dequantizationmight be combined. Alternatively, customized quantization tables may beused and signaled from an encoder to a decoder, e.g. in a bitstream. Thequantization is a lossy operation, wherein the loss increases withincreasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g. by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g. an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g. by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samples. Theloop filter unit is, e.g., configured to smooth pixel transitions, orotherwise improve the video quality. The loop filter unit 220 maycomprise one or more loop filters such as a de-blocking filter, asample-adaptive offset (SAO) filter or one or more other filters, e.g. abilateral filter, an adaptive loop filter (ALF), a sharpening, asmoothing filters or a collaborative filters, or any combinationthereof. Although the loop filter unit 220 is shown in FIG. 2 as beingan in loop filter, in other configurations, the loop filter unit 220 maybe implemented as a post loop filter. The filtered block 221 may also bereferred to as filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as sampleadaptive offset information), e.g. directly or encoded via the entropyencoding unit 270, so that, e.g., a decoder 30 may receive and apply thesame loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g. previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g. previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g. if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g. an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g. filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g. fromdecoded picture buffer 230 or other buffers (e.g. line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g. inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g. an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g. from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitionthe block 203 into smaller block partitions or sub-blocks (which formagain blocks), e.g. iteratively using quad-tree-partitioning (QT),binary partitioning (BT) or triple-tree-partitioning (TT) or anycombination thereof, and to perform, e.g., the prediction for each ofthe block partitions or sub-blocks, wherein the mode selection comprisesthe selection of the tree-structure of the partitioned block 203 and theprediction modes are applied to each of the block partitions orsub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203into smaller partitions, e.g. smaller blocks of square or rectangularsize. These smaller blocks (which may also be referred to as sub-blocks)may be further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g. partitioned into two or more blocksof a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level1, depth 1), wherein these blocks may be again partitioned into two ormore blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2,depth 2), etc. until the partitioning is terminated, e.g. because atermination criterion is fulfilled, e.g. a maximum tree depth or minimumblock size is reached. Blocks which are not further partitioned are alsoreferred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT).

As mentioned before, the term “block” as used herein may be a portion,in particular a square or rectangular portion, of a picture. Withreference, for example, to HEVC and VVC, the block may be or correspondto a coding tree unit (CTU), a coding unit (CU), prediction unit (PU),and transform unit (TU) and/or to the corresponding blocks, e.g. acoding tree block (CTB), a coding block (CB), a transform block (TB) orprediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto the PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quadtree structure similar tothe coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), a combined Quad-tree and binary tree (QTBT) partitioning is forexample used to partition a coding block. In the QTBT block structure, aCU can have either a square or rectangular shape. For example, a codingtree unit (CTU) is first partitioned by a quadtree structure. Thequadtree leaf nodes are further partitioned by a binary tree or ternary(or triple) tree structure. The partitioning tree leaf nodes are calledcoding units (CUs), and that segmentation is used for prediction andtransform processing without any further partitioning. This means thatthe CU, PU and TU have the same block size in the QTBT coding blockstructure. In parallel, multiple partition, for example, triple treepartition may be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of (e.g.pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g. non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g. as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g. non-directionalmodes like DC (or mean) mode and planar mode, or directional modes, e.g.as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g. stored in DBP 230) and other inter-prediction parameters, e.g.whether the whole reference picture or only a part, e.g. a search windowarea around the area of the current block, of the reference picture isused for searching for a best matching reference block, and/or e.g.whether pixel interpolation is applied, e.g. half/semi-pel and/orquarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct modemay be applied.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g. reconstructed blocks of one or a plurality ofother/different previously decoded pictures 231, for motion estimation.E.g. a video sequence may comprise the current picture and thepreviously decoded pictures 231, or in other words, the current pictureand the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

The motion compensation unit may also generate syntax elementsassociated with the blocks and video slices for use by video decoder 30in decoding the picture blocks of the video slice. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g. a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g. in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g. encodedbitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g. data that represents pictureblocks of an encoded video slice (and/or tile groups or tiles) andassociated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g. a summer 314), aloop filter 320, a decoded picture buffer (DBP) 330, a mode applicationunit 360, an inter prediction unit 344 and an intra prediction unit 354.Inter prediction unit 344 may be or include a motion compensation unit.Video decoder 30 may, in some examples, perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214 the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3), e.g. any or all of inter prediction parameters (e.g.reference picture index and motion vector), intra prediction parameter(e.g. intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 may be configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode application unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level. Inaddition or as an alternative to slices and respective syntax elements,tile groups and/or tiles and respective syntax elements may be receivedand/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g. by parsing and/or decoding, e.g. by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice (or tile or tile group) to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configuredto add the reconstructed residual block 313, to the prediction block 365to obtain a reconstructed block 315 in the sample domain, e.g. by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g. to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g. a bilateral filter, anadaptive loop filter (ALF), a sharpening, a smoothing filters or acollaborative filters, or any combination thereof. Although the loopfilter unit 320 is shown in FIG. 3 as being an in loop filter, in otherconfigurations, the loop filter unit 320 may be implemented as a postloop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. viaoutput 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g. by parsingand/or decoding, e.g. by entropy decoding unit 304). Mode applicationunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g.motion compensation unit) of mode application unit 360 is configured toproduce prediction blocks 365 for a video block of the current videoslice based on the motion vectors and other syntax elements receivedfrom entropy decoding unit 304. For inter prediction, the predictionblocks may be produced from one of the reference pictures within one ofthe reference picture lists. Video decoder 30 may construct thereference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in DPB 330. The same orsimilar may be applied for or by embodiments using tile groups (e.g.video tile groups) and/or tiles (e.g. video tiles) in addition oralternatively to slices (e.g. video slices), e.g. a video may be codedusing I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (e.g., intra or inter prediction) used to code the videoblocks of the video slice, an inter prediction slice type (e.g., Bslice, P slice, or GPB slice), construction information for one or moreof the reference picture lists for the slice, motion vectors for eachinter encoded video block of the slice, inter prediction status for eachinter coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for or by embodiments using tile groups (e.g. video tile groups)and/or tiles (e.g. video tiles) in addition or alternatively to slices(e.g. video slices), e.g. a video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), wherein a picture may be partitioned into or decodedusing one or more slices (typically non-overlapping), and each slice maycomprise one or more blocks (e.g. CTUs).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), wherein a picture may be partitioned into or decoded usingone or more tile groups (typically non-overlapping), and each tile groupmay comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles,wherein each tile, e.g. may be of rectangular shape and may comprise oneor more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current operation may be further processed andthen output to the next operation. For example, after interpolationfiltering, motion vector derivation or loop filtering, a furtheroperation, such as Clip or shift, may be performed on the processingresult of the interpolation filtering, motion vector derivation or loopfiltering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP modes, temporal motion vectors, and so on). For example,the value of motion vector is constrained to a predefined rangeaccording to its representing bit. If the representing bit of motionvector is bitDepth, then the range is −2{circumflex over( )}(bitDepth−1)˜2{circumflex over ( )}(bitDepth−1)−1, where“{circumflex over ( )}” means exponentiation. For example, if bitDepthis set equal to 16, the range is −32768˜32767; if bitDepth is set equalto 18, the range is −131072˜131071. For example, the value of thederived motion vector (e.g. the MVs of four 4×4 sub-blocks within one8×8 block) is constrained such that the max difference between integerparts of the four 4×4 sub-block MVs is no more than N pixels, such as nomore than 1 pixel. Here provides two methods for constraining the motionvector according to the bitDepth.

Method 1: remove the overflow MSB (most significant bit) by flowingoperations

ux=(mvx+2^(bitDepth)) % 2^(bitDepth)  (1)

mvx=(ux>=2^(bitDepth-1))?(ux−2^(bitDepth)):ux  (2)

uy=(mvy+2bitDepth) % 2^(bitDepth)  (3)

mvy=(uy>=2^(bitDepth-1))?(uy−2^(bitDepth)):uy  (4)

where mvx is a horizontal component of a motion vector of an image blockor a sub-block, mvy is a vertical component of a motion vector of animage block or a sub-block, and ux and uy indicates an intermediatevalue;

For example, if the value of mvx is −32769, after applying formula (1)and (2), the resulting value is 32767. In computer system, decimalnumbers are stored as two's complement. The two's complement of −32769is 1,0111,1111,1111,1111 (17 bits), then the MSB is discarded, so theresulting two's complement is 0111,1111,1111,1111 (decimal number is32767), which is same as the output by applying formula (1) and (2).

ux=(mvpx+mvdx+2^(bitDepth)) % 2^(bitDepth)  (5)

mvx=(ux>=2^(bitDepth-1))?(ux−2^(bitDepth)):ux  (6)

uy=(mvpy+mvdy+2^(bitDepth)) % 2^(bitDepth)  (7)

mvy=(uy>=2^(bitDepth-1))?(uy−2^(bitDepth)):uy  (8)

The operations may be applied during the sum of mvp and mvd, as shown informula (5) to (8).

Method 2: remove the overflow MSB by clipping the value

vx=Clip3(−2^(bitDepth-1),2^(bitDepth-1)−1,vx)

vy=Clip3(−2^(bitDepth-1),2^(bitDepth-1)−1,vy)

-   -   where vx is a horizontal component of a motion vector of an        image block or a sub-block, vy is a vertical component of a        motion vector of an image block or a sub-block; x, y and z        respectively correspond to three input value of the MV clipping        process, and the definition of function Clip3 is as follow:

${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{{x;}\ } & {z < x} \\{{y;}\ } & {z > y} \\{{z;}\ } & {otherwise}\end{matrix} \right.$

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations can be practiced with a single processor as shown, e.g.,the processor 502, advantages in speed and efficiency can be achievedusing more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

Parameter Sets

Parameter sets are fundamentally similar and share the same basic designgoals-namely bit rate efficiency, error resiliency, and providingsystems layer interfaces. There is a hierarchy of parameter sets in HEVC(H.265), including the Video Parameter Set (VPS), Sequence Parameter Set(SPS) and Picture Parameter Set (PPS) which are similar to theircounterparts in AVC and VVC. Each slice references a single active PPS,SPS and VPS to access information used for decoding the slice. The PPScontains information which applies to all slices in a picture, and henceall slices in a picture may require refer to the same PPS. The slices indifferent pictures are also allowed to refer to the same PPS. Similarly,the SPS contains information which applies to all pictures in the samecoded video sequence.

While the PPS may differ for separate pictures, it is common for many orall pictures in a coded video sequence to refer to the same PPS. Reusingparameter sets is bit rate efficient because it avoids the necessity tosend shared information multiple times. It is also loss robust becauseit allows parameter set content to be carried by some more reliableexternal communication link or to be repeated frequently within thebitstream to ensure that it will not get lost.

Scalable Video Coding, Layer and Video Parameter Set (VPS)

Scalable video coding provides a mechanism for coding video in multiplelayers, each layer represents a quality representation of the same videoscene. The base layer (BL) is the lowest quality representation. One ormore enhancement layers (ELs) may be coded by referencing lower layersand provide improved video quality. Decoding a subset of layers of ascalable coded video bitstream results in video with a lower but stillacceptable quality. This allows a more graceful degradation comparedwith non-scalable video bitstreams, where reduction in bitrate typicallycauses more drops in video quality.

There are multiple types of scalability exists in a scalable videosequence, including temporal scalability, spatial scalability, andquality scalability. FIG. 11 provides an example illustrating bothspatial and temporal scalability. In FIG. 11, two layers are coded indifferent resolutions. The BL has a lower resolution while the EL has ahigher resolution, and the spatial scalability is achieved by providingthe decoder to decode either the BL, EL, or both.

In addition to spatial scalability, temporal scalability is achievedwithin a coding layer. In this example, each coding layer is dividedinto two temporal sub-layers, which are labeled by temporal ID 0 and IID1, respectively. The temporal scalability is achieved by providing todecode either temporal sub-layer 0 (with temporal ID equal to 0) or bothsub-layer 0 and 1.

Pictures in each layer is assigned with layer id, e.g. with syntaxelement nuh_layer_id. A coded layer video sequence (CLVS) is a sequenceof Pictures with the same value of nuh_layer_id that comprise, indecoding order, a special coding layer video sequence starting codingpicture (CLVSS, e.g. intra picture), followed by zero or more picturesthat are not CLVSS pictures, including all subsequent pictures up to butnot including any subsequent pictures that is a CLVSS picture.

A coded video sequence (CVS) comprises one of more coded layer videosequences (CLVS). In the example of FIG. 11, assuming the first picturesof BL and EL are CLVSS picture and all other pictures are not CLVSSpictures, this CVS comprises two CLVSs.

The Sequence Parameter Set (SPS)

The SPS contains parameters that apply to one layers of a coded videosequence and do not change from picture to picture within a coded videosequence.

In some extreme cases, an SPS might be not used by any pictures in aCLVS.

It might be also be the case that an SPS is shared by different CLVSs.

In the latest VVC specification draft (i.e.http://phenix.it-sudparis.eu/jvet/doc enduser/documents/19_Teleconference/wg11/JVET-S0152-v5.zip, referred to asVVC draft in later section for simplicity), the definition of SPS is asfollows:

sequence parameter set (SPS): A syntax structure containing syntaxelements that apply to zero or more entire CLVSs as determined by thecontent of a syntax element found in the PPS referred to by a syntaxelement found in each picture header.

For definition of PPS and picture header, please refer to VVC draft.

In particular, the SPS includes information on signaling of decodedpicture buffer (i.e. dpb).

Some parts of the following table shows a snapshot of part of the dpbsignaling in SPS in VVC:

Signaling of Decoded Picture Buffer (DPB) Information.

Decoded Picture Buffer

Decoded Picture Buffer (DPB) is a buffer which is used to store thedecoded picture for reference, for example, as a reference picture forinter prediction. In an example disclosed in VVC draft, the relatedsyntax elements of parameters for DBP in sequence parameter set (SPS)are highlighted.

TABLE 1 Decoded picture related syntax elements in SPS . . .  if(sps_ptl_dpb_hrd_params_present_flag ) {   if( sps_max_sublayers_minus1 >0 )    sps_sublayer_dpb_params_flag u(1)   dpb_parameters( spsmax_sublayers_minus1, sps_sublayer_dpb_params_flag )  } . . .

sps_ptl_dpb_hrd_params_present_flag equal to 1 specifies that aprofile_tier_level( ) syntax structure and a dpb_parameters( ) syntaxstructure are present in the SPS, and a general_hrd_parameters( ) syntaxstructure and an ols_hrd_parameters( ) syntax structure may also bepresent in the SPS. sps_ptl_dpb_hrd_params_present_flag equal to 0specifies that none of these four syntax structures is present in theSPS.

When sps_video_parameter_set_id is greater than 0 and there is an OLSthat contains only one layer with nuh_layer_id equal to the nuh_layer_idof the SPS, or when sps_video_parameter_set_id is equal to 0, the valueof sps_ptl_dpb_hrd_params_present_flag shall be equal to 1.

An OLS (output layer set) is a set of layers for which one or morelayers are specified as the output layers. An output layer is a layer ofan output layer set that is output.

The syntax tables for syntax structures profile_tier_level( ),dpb_parameters( ), general_hrd_parameters( ), ols_hrd_parameters( ) canbe found in VVC draft.

A syntax element sps_max_sublayers_minus1 indicates a number ofavailable temporal sublayers. When a number of available temporalsublayers is larger than 1 (e.g. a value of syntax elementsps_max_sublayers_minus1 is greater than 0), a value of the syntaxelement sps_sublayer_dpb_params_flag is signaled in a bitstream. Thesyntax element sps_sublayer_dpb_params_flag mandates whether to signaldecode picture information for each available sublayer (when its valueis equal to 1) or to signal just for the highest temporal sublayer (whenits value is equal to 0). When a value of sps_sublayer_dpb_params_flagis not present, e.g. there is only one temporal sublayer (a value ofsps_max_sublayers_minus1==0), the value of sps_max_sublayers_minus1 isinferred as 0.

In some examples, a value of syntax elementsps_ptl_dpb_hrd_params_present_flag indicates whether a signalingstructure dpb_parameter( ) is signaled in SPS or not. When a value ofsyntax element sps_ptl_dpb_hrd_params_present_flag is equal to 1, thesignaled date structure dpb_parameter( ) is invoked, with the number ofavailable temporal sublayers minus 1 (sps_max_sublayers_minus1) and theflag sps_sublayer_dpb_params_flag as the first and second parameter,respectively.

In an example, the signaling structure of dpb_parameter( ) in VVC draftis defined as follows.

TABLE 2 definition of dpb_parameters syntax structure dpb_parameters(maxSubLayersMinus1, subLayerInfoFlag ) { Descriptor  for( i = (subLayerInfoFlag ? 0 : maxSubLayersMinus1 );   i <= maxSubLayersMinus1;i++ ) {  max_dec_pic_buffering_minus1[ i ] ue(v)  max_num_reorder_pics[i ] ue(v)  max_latency_increase_plus1[ i ] ue(v)  } }

The dpb_parameters( ) syntax structure provides information of DPB size,maximum picture reorder number, and maximum latency for one or moreOLSs.

When a dpb_parameters( ) syntax structure is included in a VPS, the OLSsto which the dpb_parameters( ) syntax structure applies are specified bythe VPS. When a dpb_parameters( ) syntax structure is included in anSPS, it applies to the OLS that includes only the layer that is thelowest layer among the layers that refer to the SPS, and this lowestlayer is an independent layer.

max_dec_pic_buffering_minus1[i] plus 1 specifies the maximum requiredsize of the DPB in units of picture storage buffers when Htid is equalto i. The value of max_dec_pic_buffering_minus1[i] shall be in the rangeof 0 to MaxDpbSize−1, inclusive, where MaxDpbSize is as specified inclause A.4.2. When i is greater than 0, max_dec_pic_buffering_minus1[i]shall be greater than or equal to max_dec_pic_buffering_minus1[i−1].When max_dec_pic_buffering_minus1[i] is not present for i in the rangeof 0 to maxSubLayersMinus1−1, inclusive, due to subLayerInfoFlag beingequal to 0, it is inferred to be equal tomax_dec_pic_buffering_minus1[maxSubLayersMinus1].

max_num_reorder_pics[i] specifies the maximum allowed number of picturesof the OLS that can precede any picture in the OLS in decoding order andfollow that picture in output order when Htid is equal to i. The valueof max_num_reorder_pics[i] shall be in the range of 0 tomax_dec_pic_buffering_minus1[i], inclusive. When i is greater than 0,max_num_reorder_pics[i] shall be greater than or equal tomax_num_reorder_pics[i−1]. When max_num_reorder_pics[i] is not presentfor i in the range of 0 to maxSubLayersMinus1−1, inclusive, due tosubLayerInfoFlag being equal to 0, it is inferred to be equal tomax_num_reorder_pics[maxSubLayersMinus1].

max_latency_increase_plus1[i] not equal to 0 is used to compute thevalue of MaxLatencyPictures[i], which specifies the maximum number ofpictures in the OLS that can precede any picture in the OLS in outputorder and follow that picture in decoding order when Htid is equal to i.

When max_latency_increase_plus1[i] is not equal to 0, the value ofMaxLatencyPictures[i] is specified as follows:

MaxLatencyPictures[i]=max_num_reorder_pics[i]+max_latency_increase_plus1[i]−1  (112)

When max_latency_increase_plus1[i] is equal to 0, no corresponding limitis expressed.

The value of max_latency_increase_plus1[i] shall be in the range of 0 to2³²−2, inclusive. When max_latency_increase_plus1[i] is not present fori in the range of 0 to maxSubLayersMinus1−1, inclusive, due tosubLayerInfoFlag being equal to 0, it is inferred to be equal tomax_latency_increase_plus1[maxSubLayersMinus1].

More detailed information for the syntax elements and variables used toexplain the dpb parameters (max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i]) please referto VVC draft.

The dpb_parameters signaling structure either signals one sublayer'sdecoded picture buffer information or each sublayer's decoded pictureinformation, controlled by the value of subLayerInfoFlag. When a valueof subLayerInfoFlag is 0, the decoded picture buffer information of thehighest sublayer among the available temporal sublayers is signaled(i=maxSubLayersMinus1). When a value of subLayerInfoFlag is 1, thedecoded picture buffer information of each sublayer among the availabletemporal sublayers is signaled (a value of i ranges from 0 tomaxSubLayersMinus1, inclusive).

Problem about the Semantics of Syntax Elementsps_sublayer_dpb_params_flag

In the VVC draft, the semantics of sps_sublayer_dpb_params_flag isdefined as follows:

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS. When not present, the value ofsps_sub_dpb_params_info_present_flag is inferred to be equal to 0.

The above semantics has two issues. First, there has been a typo in thelast sentence.

When not present, the value of sps_sub_dpb_params_info_present_flag isinferred to be equal to 0.

sps_sub_dpb_params_info_present_flag is not defined anywhere else andthe last sentence shall be modified as follows:

When not present, the value of sps_sublayer_dpb_params_flag is inferredto be equal to 0.

Second, the semantics of sps_sublayer_dpb_params_flag is not preciseenough. Because the range of i in max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] is notdefined. It can be observed from Table 2 that when i is equal tomaxSubLayersMinus1 (corresponding to sps_max_sublayers_minus1 in Table1), no matter sps_sublayer_dpb_params_flag is equal to 0 or 1, thesyntax elements max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] are alwayssignaled. sps_sublayer_dpb_params_flag doesn't control the presence ofmax_dec_pic_buffering_minus1 [i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] in this case, which is in contradiction tothe current definition.

In some examples, the syntax element sps_sublayer_dpb_params_flag isused only as the second parameter of the dpb_parameters.

For the following embodiments, we suppose the typo (the first issue) isfixed already, and the proposed embodiments focus on addressing thesecond issue, inaccurate semantic of sps_sublayer_dpb_params_flag.

Embodiment 1

According to the first embodiment, the semantics ofsps_sublayer_dpb_params_flag is modified as follows:

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0. When sps_max_sublayers_minus1 is equal to 0, the value ofsps_sublayer_dpb_params_flag is inferred to be equal to 0, andmax_dec_pic_buffering_minus1[0], max_num_reorder_pics[0], andmax_latency_increase_plus1[0] is always signaled for the only sublayerreferred to the SPS.

In this way, the semantics of sps_sublayer_dpb_params_flag is clarified.Only when there are more than one sublayers (sps_max_sublayers_minus1 islarger than 0), it controls the presence of minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] indpb_parameters( ) syntax structure for i range from 0 tosps_max_sublayers_minus1−1. Otherwise (sps_max_sublayers_minus1 is equalto 0), the signaling of max_dec_pic_buffering_minus1[0],max_num_reorder_pics[0], and max_latency_increase_plus1[0] is alwayssignalled, no matter which value sps_sublayer_dpb_params_flag isrepresented. Therefore, the semantics might also be changed as followsin Embodiment 2.

Embodiment 2

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0. When sps_max_sublayers_minus1 is equal to 0, the value ofsps_sublayer_dpb_params_flag is inferred to be equal to 1, andmax_dec_pic_buffering_minus1[0], max_num_reorder_pics[0], andmax_latency_increase_plus1[0] is always signaled for the only sublayerreferred to the SPS.

Or even remove the inference rule for the value ofsps_sublayer_dpb_params_flag, as shown in Embodiment 3.

Embodiment 3

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0. When sps_max_sublayers_minus1 is equal to 0,max_dec_pic_buffering_minus1[0], max_num_reorder_pics[0], andmax_latency_increase_plus1[0] is always signaled for the only sublayerreferred to the SPS.

Or with some explanation when sps_max_sublayers_minus1 is equal to 0 asshown in Embodiment 4.

Embodiment 4

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0. When sps_max_sublayers_minus1 is equal to 0, the value ofsps_sublayer_dpb_params_flag is meaningless, andmax_dec_pic_buffering_minus1[0], max_num_reorder_pics[0], andmax_latency_increase_plus1[0] is always signaled for the only sublayerreferred to the SPS.

The data structure dpb_parameter ( ) is not only invoked in SPS, butalso might be invoked in VPS. The following is a snapshot of VPS wheredpb_parameter( ) is invoked.

TABLE 3 dpb_parameters syntax structure in VPS for( i = 0; i <VpsNumDpbParams; i++ ) {  if( !vps_default_ptl_dpb_hrd_max_tid_flag )  vps_dpb_max_tid[ i ] u(3)  dpb_parameters( vps_dpb_max_tid[ i ]   vps_sublayer_dpb_params_present_flag ) }

Wherein specifying the number of dpb_parameters( ) syntax structures inthe VPS.

vps_default_ptl_dpb_hrd_max_tid_flag equal to 1 specifies that thesyntax elements vps_ptl_max_tid[i], vps_dpb_max_tid[i], and vpshrd_max_tid[i] are not present and are inferred to be equal to thedefault value vps_max_sublayers_minus1. vps_default_ptl_dpb_hrd_max_tidflag equal to 0 specifies that the syntax elements vps_ptl_max_tid[i],vps_dpb_max_tid[i], and vps_ptl_max_tid[i] are present. When notpresent, the value of vps_default_ptl_dpb_hrd_max_tid_flag is inferredto be equal to 1.

For detailed explanation of vps_ptl_max_tid[i] and vps_hrd_max tid[i]please refer to VVC draft.

vps_dpb_max_tid[i] specifies the TemporalId of the highest sublayerrepresentation for which the DPB parameters may be present in the i-thdpb_parameters( ) syntax strutcure in the VPS. The value ofvps_dpb_max_tid[i] shall be in the range of 0 tovps_max_sublayers_minus1, inclusive. When not present, the value ofvps_dpb_max_tid[i] is inferred to be equal to vps_max_sublayers_minus1,and

vps_sublayer_dpb_params_present_flag is used to control the presence ofmax_dec_pic_buffering_minus1[ ], max_num_reorder_pics[ ], andmax_latency_increase_plus1[ ] syntax elements in the dpb_parameters( )syntax structures in the VPS. When not present,vps_sub_dpb_params_info_present_flag is inferred to be equal to 0.

The semantics of vps_sublayer_dpb_params_present_flag has a similarissue with the semantics of sps_sublayer_dpb_params_flag, as describedbefore.

The size of syntax element array max_dec_pic_buffering_minus1[ ],max_num_reorder_pics[ ], and max_latency_increase_plus1[ ] is notdefined in the semantics. It can be observed from Table 2 that whenthere is only one sublayer (corresponding to vps_dpb_max_tid[i] in Table4 equal to 0), no matter vps_sublayer_dpb_params_present_flag is equalto 0 or 1, the syntax elements max_dec_pic_buffering_minus1[ ],max_num_reorder_pics[ ], and max_latency_increase_plus1[ ] are alwayssignaled. vps_sublayer_dpb_params_present_flag doesn't control thepresence of max_dec_pic_buffering_minus1[ ], max_num_reorder_pics[ ],and max_latency_increase_plus1[ ] in this case, which is contradict tothe current definition.

Embodiment 9

In one example, the semantics of vps_sublayer_dpb_params_present_flag ismodified as follows:

vps_sublayer_dpb_params_present_flag is used to control the presence ofmax_dec_pic_buffering_minus1[j], max_num_reorder_pics[j], andmax_latency_increase_plus1[j] syntax elements in the dpb_parameters( )syntax structure in the VPS for j in range from 0 tovps_dpb_max_tid[i]−1, inclusive, when vps_dpb_max_tid[i] in VPS islarger than 0. When not present, vps_sub_dpb_params_info_present_flag isinferred to be equal to 0.

It is noted that j instead of i is used for specifying the range ofsyntax element array max_dec_pic_buffering_minus1[ ],max_num_reorder_pics[ ], and max_latency_increase_plus1[ ] in order toavoid confusion of the i in vps_dpb_max_tid[i].

Remark, Problem 2 and corresponding solutions, dependentFlag etc.

When inter prediction is performed, a reference picture can be a decodedpictures from the same layer, or a reference picture from a lower layer.In the latter case, the reference picture in a low layer is calledinter-layer reference picture (ILRP), and the lower layer that containsone or more ILRP is called a reference (or dependent) layer.

To support inter-layer prediction, several intermediate variables areused according to the syntax elements signaled in VPS. For example, inequation 37 of the VVC draft, a derivation process for variablesdependencyFlag[i][j], NumDirectRefLayers[i], DirectRefLayerIdx[i][d],NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j] isdefined as follows:

The variables dependencyFlag[i][j], NumDirectRefLayers[i],DirectRefLayerIdx[i][d], NumRefLayers[i], RefLayerIdx[i][r], andLayerUsedAsRefLayerFlag[j] are derived as follows:

for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0;j <= vps_max_layers_minus1; j++ ) {   dependencyFlag[ i ][ j ] =vps_direct_ref_layer_flag[ i ][ j ]   for( k = 0; k < i; k++ )    if(vps_direct_ref_layer_flag[ i ][ k ] && dependencyFlag[ k ][ j ] )    dependencyFlag[ i ][ j ] = 1  }  LayerUsedAsRefLayerFlag[ i ] = 0 }for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r =0; j <= vps_max_layers_minus1; j++ ) {   (37)   if(vps_direct_ref_layer_flag[ i ][ j ] ) {    DirectRefLayerIdx[ i ][ d++ ]= j    LayerUsedAsRefLayerFlag[ j ] = 1   }   if( dependencyFlag[ i ][ j] )    RefLayerIdx[ i ][ r++ ] = j  }  NumDirectRefLayers[ i ] = d NumRefLayers[ i ] = r }

dependencyFlag[i][j] equal to 1 specifies that the layer with index j isa reference layer for the layer with index i. dependencyFlag[i][j] equalto 0 specifies that the layer with index j is a not reference layer forthe layer with index i.

The dependency between a layer with index i and its reference layer jcan be direct or indirect. If the j-th layer is a direct dependent layerof i-th layer, the dependencies is signaled with syntax elementvps_direct_ref_layer_flag[i][j] for range i from 0 to, and for j from 0to i−1 in VPS. As shown in Table 4, with syntax elements irrelevant tothis embodiment of the disclosure removed:

for( i = 0; i <= vps_max_layers_minus1; i++ ) }  . . . u(6)  if( i > 0&& !vps_all_independent_layers_flag ) {   vps_independent_layer_flag[ i] u(1)   if( !vps_independent_layer_flag[ i ] ) {    . . . u(1)    for(j = 0; j < i; j++ ) {     vps_direct_ref_layer_flag[ i ][ j ] u(1)     . . .    }   }  }

The above syntax table shows when not all layers are independent layers,how VPS signaled the dependency between layers.

vps_max_layers_minus1 stands for is the maximum allowed number of layersin each CVS referring to the VPS. The layer dependency information issignaled only from the second lowest layer (i.e. i=1) and when not alllayer are independent layer, indicated by syntax elementvps_all_independent_layers_flag.

vps_all_independent_layers_flag equal to 1 specifies that all layersspecified by the VPS are independently coded without using inter-layerprediction. vps_all_independent_layers_flag equal to 0 specifies thatone or more of the layers specified by the VPS may use inter-layerprediction. When not present, the value ofvps_all_independent_layers_flag is inferred to be equal to 1.

In VVC, the lowest layer (i.e. corresponding tovps_independent_layer_flag[0]) is always an independent layer. So thesyntax element vps_independent_layer_flag[i] is signaled from the secondlowest layer (i.e. vps_independent_layer_flag[1]), and its semantics isquit straight forward.

vps_independent_layer_flag[i] equal to 1 specifies that the layer withindex i does not use inter-layer prediction.vps_independent_layer_flag[i] equal to 0 specifies that the layer withindex i may use inter-layer prediction and the syntax elementsvps_direct_ref_layer_flag[i][j] for j in the range of 0 to i−1,inclusive, are present in VPS. When not present, the value ofvps_independent_layer_flag[i] is inferred to be equal to 1.

Only when a layer is not an independent layer (i.e.vps_independent_layer_flag[i] is 0), then its direct dependent layer issignaled, indicated by vps_direct_ref_layer_flag[i][j], forj ranges from0 to i−1.

The semantics of vps_direct_ref_layer_flag[i][j] is defined as follows:

vps_direct_ref_layer_flag[i][j] equal to 0 specifies that the layer withindex j is not a direct reference layer for the layer with index i.vps_direct_ref_layer_flag [i][j] equal to 1 specifies that the layerwith index j is a direct reference layer for the layer with index i.When vps_direct_ref_layer_flag[i][j] is not present for i and j in therange of 0 to vps_max_layers_minus1, inclusive, it is inferred to beequal to 0. When vps_independent_layer_flag[i] is equal to 0, thereshall be at least one value of j in the range of 0 to i−1, inclusive,such that the value of vps_direct_ref_layer_flag[i][j] is equal to 1.

When a layer is a dependent layer (i.e. itsvps_independent_layer_flag[i] is equal to 0), the constraint in thesemantics of vps_direct_ref_layer_flag[i][j] specifies that at least oneof its lower layers j in the range of 0 to i−1, inclusive, shall be areference layer for layer i.

In the case of indirect dependency, it can occur when a layer i directdepends on layer k (k<i) and the layer k in turn depends on layer j(j<k). In such case, the layer with index i is dependent on layer j, andthe corresponding dependencyFlag[i][j] is equal to 1.

Problem of the derivation process. Because only a layer can only dependon a lower layer, the loop of looking for dependent lower layer j in thederivation process can be simplified. It doesn't necessary for loop overall layer in VPS, but only the layers that are lower than the currentlayer i.

Embodiment 5

In one example, the derivation process of variablesdependencyFlag[i][j], NumDirectRefLayers[i], DirectRefLayerIdx[i][d],NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j] ismodified as follows:

The variables dependencyFlag[i][j], NumDirectRefLayers[i],DirectRefLayerIdx[i][d], NumRefLayers[i], RefLayerIdx[i][r], andLayerUsedAsRefLayerFlag[j] are derived as follows:

for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0; j < i; j++) {   dependencyFlag[ i ][ j ] = vps_direct_ref_layer_flag[ i ][ j ]  for( k = 0; k < i; k++ )    if( vps_direct_ref_layer_flag[ i ][ k] && dependencyFlag[ k ][ j ] )     dependencyFlag[ i ][ j ] = 1  } LayerUsedAsRefLayerFlag[ i ] = 0 } for( i = 0;i <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r = 0; j <i; j++) { (37)   if( vps_direct_ref_layer_flag[ i ][ j ] ) {   DirectRefLayerIdx[ i ][ d++ ] = j    LayerUsedAsRefLayerFlag[ j ] = 1  }   if( dependencyFlag[ i ][ j ] )    RefLayerIdx[ i ][ r++ ] = j  } NumDirectRefLayers[ i ] = d  NumRefLayers[ i ] = r }

Embodiment 6

In another example, the derivation process of variablesdependencyFlag[i][j], NumDirectRefLayers[i], DirectRefLayerIdx[i][d],NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j] ismodified as follows:

The variables dependencyFlag[i][j], NumDirectRefLayers[i],DirectRefLayerIdx[i][d], NumRefLayers[i], RefLayerIdx[i][r], andLayerUsedAsRefLayerFlag[j] are derived as follows:

for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0; j <1; j++ ){   dependencyFlag[ i ][ j ] = vps_direct_ref_layer_flag[ i ][ j ]  for( k = j+1; k < i; k++ )    if( vps_direct_ref_layer_flag[ i ][ k] && dependencyFlag[ k ][ j ] )     dependencyFlag[ i ][ j ] = 1  } LayerUsedAsRefLayerFlag[ i ] = 0 } for( i = 0;i <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r = 0; j <i; j++) { (37)   if( vps_direct_ref_layer_flag[ i ][ j ] ) {   DirectRefLayerIdx[ i ][ d++ ] = j    LayerUsedAsRefLayerFlag[ j ] = 1  }   if( dependencyFlag[ i ][ j ] )    RefLayerIdx[ i ][ r++ ] = j  } NumDirectRefLayers[ i ] = d  NumRefLayers[ i ] = r }

Embodiment 7

In another example, the derivation process of variablesdependencyFlag[i][j], NumDirectRefLayers[i], DirectRefLayerIdx[i][d],NumRefLayers[i], RefLayerIdx[i][r], and LayerUsedAsRefLayerFlag[j] ismodified as follows:

The variables dependencyFlag[i][j], NumDirectRefLayers[i],DirectRefLayerIdx[i][d], NumRefLayers[i], RefLayerIdx[i][r], andLayerUsedAsRefLayerFlag[j] are derived as follows:

for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0; j <=vps_max_layers_minus1; j++ ) {   dependencyFlag[ i ][ j ] =vps_direct_ref_layer_flag[ i ][ j ]   for( k = j+1; k < i; k++ )    if(vps_direct_ref_layer_flag[ i ][ k ] && dependencyFlag[ k ][ j ])    dependencyFlag[ i ][ j ] = 1  }  LayerUsedAsRefLayerFlag[ i ] = 0 }for( i = 0; i <= vps_max_layers_minus1; i++ ) {  for( j = 0, d = 0, r =0; j <= vps_max_layers_minus1; j++ ) { (37)   if(vps_direct_ref_layer_flag[ i ][ j ] ) {    DirectRefLayerIdx[ i ][ d++ ]= j    LayerUsedAsRefLayerFlag[ j ] = 1   }   if( dependencyFlag[ i ][ j] )    RefLayerIdx[ i ][ r++ ] = j  }  NumDirectRefLayers[ i ] = d NumRefLayers[ i ] = r }

Only the loop for (k=0; k<i; k++) is modified to for (k=j+1; k<i; k++).

Embodiment 8

correspondingly, the semantics of vps_direct_ref_layer_flag[i][j] ischanged as follows:

vps_direct_ref_layer_flag[i][j] equal to 0 specifies that the layer withindex j is not a direct reference layer for the layer with index i.vps_direct_ref_layer_flag [i][j] equal to 1 specifies that the layerwith index j is a direct reference layer for the layer with index i.When vps_direct_ref_layer_flag[i][j] is not present for i in the rangeof 1 to vps_max_layers_minus1 and for j in the range of 0 to i−1, bothinclusive, it is inferred to be equal to 0. Whenvps_independent_layer_flag[i] is equal to 0, there shall be at least onevalue of j in the range of 0 to i−1, inclusive, such that the value ofvps_direct_ref_layer_flag[i][j] is equal to 1.

There are several other variables syntax elements expressing thedependency similar as vps_direct_ref_layer_flag[i][j], their range shallbe changed in the same way.

In accordance with the description above a method of decoding a videobitstream and a method of encoding a video bitstream are providedherein. Correspondingly, an apparatus for decoding a (coded) videobitstream and an apparatus for decoding a video bitstream are providedherein.

FIG. 14 illustrates a method of decoding a video bitstream implementedby a decoding device, wherein a sequence parameter set, SPS, is coded inthe video bitstream and contains syntax elements that apply to a videosequence. The method comprises obtaining 1410 (for example, by parsingthe bitstream) a value of a first syntax element (for example,sps_ptl_dpb_hrd_params_present_flag according to the description above)from the SPS, wherein the value of the first syntax element is used tospecify whether a decoded picture buffer, DPB, parameters syntaxstructure is present in the SPS. The method further comprises obtaining1420 (for example, by parsing the bitstream) a value of a second syntaxelement (for example, sps_sublayer_dpb_params_flag according to thedescription above) from the SPS, at least when determining (it isdetermined) that the value of the first syntax element specifies thatthe DPB parameters syntax structure is present in the SPS, wherein thevalue of the second syntax element is used to specify the presence of aDPB syntax element (for example, one of max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] according tothe detailed description above) in the DPB parameters syntax structure,wherein the DPB syntax element is applied to a temporal sublayer exceptfor the highest temporal sublayer in the video sequence.

It is noted that the bitstream may be obtained by means of a wirelessnetwork or wired network. The bitstream may be transmitted from awebsite, server, or other remote source using a coaxial cable, fiberoptic cable, twisted pair, digital subscriber line (DSL), or wirelesstechnologies such as infrared, radio, microwave, WIFI, Bluetooth, LTE or5G.

The bitstream may be a sequence of bits, in the form of a networkabstraction layer (NAL) unit stream or a byte stream, that forms therepresentation of a sequence of access units (AUs) forming one or morecoded video sequences (CVSs).

In a specific example, the bitstream formats specifies the relationshipbetween a network abstraction layer (NAL) unit stream and a byte stream,either of which are referred to as the bitstream.

The bitstream can be in one of two formats: the NAL unit stream formator the byte stream format. The NAL unit stream format is conceptuallythe more “basic” type. The NAL unit stream format comprises a sequenceof syntax structures called NAL units. This sequence is ordered indecoding order. There are constraints imposed on the decoding order (andcontents) of the NAL units in the NAL unit stream.

The byte stream format can be constructed from the NAL unit streamformat by ordering the NAL units in decoding order and prefixing eachNAL unit with a start code prefix and zero or more zero-valued bytes toform a stream of bytes. The NAL unit stream format can be extracted fromthe byte stream format by searching for the location of the unique startcode prefix pattern within this stream of bytes.

FIG. 15 illustrates a method of encoding a video bitstream implementedby an encoding device, wherein a sequence parameter set, SPS, is encodedin the video bitstream and contains syntax elements that apply to avideo sequence. The method comprises determining the presence of adecoded picture buffer, DPB, parameters syntax structure in the SPS1510. A value of a first syntax element (for example,sps_ptl_dpb_hrd_params_present_flag according to the description above)is encoded 1520 into the SPS based on the determining of the presence ofthe DPB parameters syntax structure in the SPS, wherein the value of thefirst syntax element is used to specify whether the DPB parameterssyntax structure is present in the SPS. Further, the method illustratedin FIG. 15 comprises determining 1530 the presence of a DPB syntaxelement (for example, one of max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] according tothe detailed description above) in the DPB parameters syntax structure,when determining (it is determined, for example, only when it isdetermined)) that the DPB parameters syntax structure is present in theSPS in operation 1510, wherein the DPB syntax element is applied to atemporal sublayer except for the highest temporal sublayer in the videosequence. A value of a second syntax element (for example,sps_sublayer_dpb_params_flag according to the description above) isencoded 1540 into the SPS based on the determining of the presence ofthe DPB syntax element in the DPB parameters syntax structure, whereinthe value of the second syntax element is used to specify the presenceof the DPB syntax element in the DPB parameters syntax structure.

The above-described methods may be implanted in a video decodingapparatus or video encoding apparatus (producing a bitstream),respectively, as described in the following.

As shown in FIG. 16 a video decoding apparatus 1600 provided hereinaccording to an embodiment comprises an obtaining unit 1610 (forexample, comprising a parser) and a determining unit 1620. As shown inFIG. 17, an video encoding apparatus 1700 provided herein according toan embodiment comprises a determining unit 1710 and an encoding unit1720.

The obtaining unit 1610 comprised in the video decoding apparatus 1600shown in FIG. 16 is configured to obtain a value of a first syntaxelement (for example, sps_ptl_dpb_hrd_params_present_flag according tothe description above) from the SPS, wherein the value of the firstsyntax element is used to specify whether a decoded picture buffer, DPB,parameters syntax structure is present in a SPS coded in the videobitstream. The determining unit 1620 comprised in the video decodingapparatus 1600 shown in FIG. 16 is configured to determine whether thevalue of the first syntax element specifies that the DPB parameterssyntax structure is present in the SPS. Further, the obtaining unit 1610is configured to obtain a value of a second syntax element (for example,sps_sublayer_dpb_params_flag according to the description above) fromthe SPS, at least when determining (it is determined) that the value ofthe first syntax element specifies that the DPB parameters syntaxstructure is present in the SPS, wherein the value of the second syntaxelement is used to specify the presence of a DPB syntax element (forexample, one of max_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], and max_latency_increase_plus1[i] according tothe detailed description above) in the DPB parameters syntax structure,wherein the DPB syntax element is applied to a temporal sublayer exceptfor the highest temporal sublayer in the video sequence.

The determining unit 1710 comprised in the video encoding apparatus 1700shown in FIG. 17 is configured to determine the presence of a decodedpicture buffer, DPB, parameters syntax structure in a SPS. The encodingunit 1720 comprised in the video encoding apparatus 1700 shown in FIG.17 is configured to encode a value of a first syntax element (forexample, sps_ptl_dpb_hrd_params_present_flag according to thedescription above) into the SPS based on the determining of the presenceof the DPB parameters syntax structure in the SPS, wherein the value ofthe first syntax element is used to specify whether the DPB parameterssyntax structure is present in the SPS. Further, the determining unit1710 is configured to determine the presence of a DPB syntax element(for example, one ofmax_dec_pic_buffering_minus1[i],max_num_reorder_pics[i], andmax_latency_increase_plus1[i] according to the detailed descriptionabove) in the DPB parameters syntax structure, when determining (it isdetermined, for example, only when it is determined) that the DPBparameters syntax structure is present in the SPS, wherein the DPBsyntax element is applied to a temporal sublayer except for the highesttemporal sublayer in the video sequence. Further, the encoding unit 1720is configured to encode a value of a second syntax (for example,sps_sublayer_dpb_params_flag according to the description above) elementinto the SPS based on the determining of the presence of the DPB syntaxelement in the DPB parameters syntax structure, wherein the value of thesecond syntax element is used to specify the presence of the DPB syntaxelement in the DPB parameters syntax structure.

The video decoding apparatus 1600 shown in FIG. 16 may be or may becomprised by the decoder 30 shown in FIGS. 1A, 1B, and 3 and the videodecoder 3206 shown in FIG. 9. Moreover, the decoding device 1700 may becomprised by the video coding device 400 shown in FIG. 4, the apparatus500 shown in FIG. 5 and the terminal device 3106 shown in FIG. 8. Theencoding device 1700 shown in FIG. 17 may be or may be comprised by theencoder 20 shown in FIGS. 1A, 1B and 3. Further, the encoding device1700 may be comprised by the video coding device 400 shown in FIG. 4,the apparatus 500 shown in FIG. 5 and the capture device 3102 shown inFIG. 8.

In particular, the SPS includes information on signaling of subpicture.

Some parts of the following Table shows a snapshot of part of thesubpicture signaling in SPS in ITU JVET-Q200T-v13, with the downloadlink as follows:

http://phenix.it-sudparis.eu/jvet/doc_end_user/documents/17_Brussels/wg11/JVET-Q2001-v13.zip.In the remaining part of the application this document will be named VVCdraft 8 for simplicity.

seq_parameter_set_rbsp( ) { Descriptor  sps_seq_parameter_set_id u(4) sps_video_parameter_set_id u(4)  sps_max_sublayers_minus1 u(3) sps_reserved_zero_4bits u(4)  sps_ptl_dpb_hrd_params_present_flag u(1) if( sps_ptl_dpb_hrd_params_present_flag )   profile_tier_level( 1,sps_max_sublayers_minus1 )  gdr_enabled_flag u(1)  chroma_format_idcu(2)  if( chroma_format_idc == 3)   separate_colour_plane_flag u(1) res_change_in_clvs_allowed_flag u(1)  pic_width_max_in_luma_samplesue(v)  pic_height_max_in_luma_samples ue(v)  sps_conformance_window_flagu(1)  if( sps_conformance_window_flag) {   sps_conf_win_left_offsetue(v)   sps_conf_win_right_offset ue(v)   sps_conf_win_top_offset ue(v)  sps_conf_win_bottom_offset ue(v)  }  sps_log2_ctu_size_minus5 u(2) subpic_info_present_flag u(1)  if( subpic info_present flag) {  sps_num_subpics_minus1 ue(v)   sps_independent_subpics_flag u(1)  for( i = 0; sps_num_subpics_minus1 > && i <= sps_num_subpics_minus 1;i++ ) {    if( i > 0 && pic_width_max_in_luma_samples > CtbSizeY )    subpic_ctu_top_left_x[ i ] u(v)    if( i > 0 &&pic_height_max_in_luma_samples > CtbSizeY ) {     subpic_ctu_top_left_y[i ] u(v)    if( i < sps_num_subpics_minus1 &&     pic_width_max_in_luma_samples > CtbSizeY )     subpic_width_minus1[i ] u(v)    if( i < sps_num_subpics_minus1 &&     pic_height_max_in_luma_samples > CtbSizeY )    subpic_height_minus1[ i ] u(v)    if( !sps_independent_subpics_flag){     subpic_treated_as_pic_flag[ i ] u(1)    loop_filter_across_subpic_enabled_flag[ i ] u(1)    }   } . . . . ..

Some syntax elements in SPS signal the position information and thecontrol flags of each subpicture. The position information for the i-thsubpicture includes:

-   -   subpic_ctu_top_left_x[i], indicating the horizontal component of        the top-left coordinate of the subpicture i in the picture; or    -   subpic_ctu_top_left_y[i] indicating the vertical component of        the top-left coordinate of the subpicture i in the picture; or    -   subpic_width_minus1[i] indicating width of the subpicture i in        the picture; or    -   subpic_height_minus1[i] indicating height of the subpicture i in        the picture.

Some syntax elements indicate the number of subpictures inside thepicture, e.g. sps_num_subpics_minus1.

Partitioning of a picture into CTUs, slices, tiles and subpictures

Partitioning of the Picture into CTUs

Picture is divided into a sequence of coding tree units (CTUs). The termCTU is sometimes used interchangeably as CTB (coding tree block). In anexample, the term CTU is same as the CTU definition in the ITU-T H.265.For a picture that has three sample arrays, a CTU comprises an N×N blockof luma samples, and two corresponding blocks of chroma samples. FIG. 6shows an example of a picture divided into CTUs. The size of CTUs mayrequire to be the same except for the CTUs located at the pictureboundaries (where incomplete CTUs can be present).

Partitioning of the Picture into Tiles

In some examples, when tiles are enabled, picture is divided intorectangular-shaped groups of CTUs separated by vertical and/orhorizontal boundaries. The vertical and horizontal tile boundariesintersect the picture from to bottom and from left picture boundary toright picture boundary respectively. Indications information related tothe position of the horizontal tile boundaries and vertical tileboundaries are coded in bitstream.

FIG. 7 exemplifies partitioning of a picture into 9 tiles. In thisexample, the tile boundaries are marked with bold dashed lines.

When there are more than 1 tile dividing a picture vertically, the scanorder of the CTUs is changed with respect to the raster scan order ofCTUs in the picture. The CTUs are scanned according to the followingrule:

1. Tiles are scanned from left to right and from top to bottom in rasterscan order, which is called the tile scan order. This means thatstarting from the top-left tile, first all tiles in the same tile roware scanned from left to right. Then starting with the first tile in thesecond tile row (the tile row that is one below), all tiles in thesecond tile row are scanned from left to right. The process is repeatedtill all tiles are scanned.

2. For a tile, CTUs in this tile are scanned in raster scan order. Foreach CTU row, CTUs are scanned from left to right and CTU rows arescanned from top to bottom. The FIG. 7 exemplifies the scanning order ofCTUs in the tiles, the numbers correspond to the CTUs indicate thescanning order.

The tile provides a partitioning of a picture in such a way that eachtile is independently decodable from other tiles of the same picture,where decoding refers to entropy, residual, and predictive decoding.Moreover with tiles it is possible to partition the picture into similarsized regions. Therefore it is possible to process the tiles of apicture in parallel to each other, which is preferable for multi-coreprocessing environments where each processing core is identical to eachother.

The terms processing order and scanning order are used as follows in theapplication:

Processing refers to encoding or decoding of CTUs in the encoder ordecoder. Scanning order relates to the indexing of the particularpartition in a picture. The CTUs are indexed in increasing order in apicture according to a specified scan order. CTU scan order in tilemeans how the CTUs inside a tile is indexed, which might not be the sameorder in which they are processed (i.e. processing order).

Partitioning of the Picture into Slices

The slice concept provides a partitioning of a picture in such a waythat each slice is independently decodable from other slices of the samepicture, where decoding refers to entropy, residual, and predictivedecoding. The difference to tiles is that slices can have arbitraryshapes that are not necessarily rectangular (more flexible inpartitioning possibilities), and the purpose of slice partitioning isnot parallel processing but packet size matching in transmissionenvironments and error resilience.

A slice may comprise a complete picture or comprises a part of apicture. In ITU-T H.265, a slice comprises consecutive CTUs of a picturein processing order. The slice is identified according to a starting CTUaddress, the starting CTU address is signalled in a slice header or in apicture parameter set or in other unit. In an example the slice might beidentified according to a starting tile address when the slices arerequired to comprise integer number of tiles.

In the draft 8 of VVC, a slice comprises an integer number of tiles oran integer number of consecutive CTU rows within a tile of a picture.Consequently, a vertical slice boundary is also a vertical tileboundary. It is possible that a horizontal boundary of a slice is not atile boundary, horizontal CTU boundaries may be comprised within a tile;in an example, when a tile is split into multiple rectangular slices,each slice comprises an integer number of consecutive complete CTU rowswithin the tile.

In some examples, there are two slice modes, the raster-scan slice modeand the rectangular slice mode. In the raster-scan slice mode, a slicecomprises a sequence of tiles in a tile raster scan of a picture. In therectangular slice mode, a slice comprises a number of tiles thatcollectively form a rectangular region of the picture, or a slicecomprises a number of consecutive CTU rows of one tile that collectivelyform a rectangular region of the picture. Tiles within a rectangularslice are scanned in tile raster scan order within the rectangularregion corresponding to that slice.

All slices of a picture collectively form the entire picture, i.e. allCTUs of a picture are comprised in one of the slices of a picture.Similar rules apply for tiles and subpictures.

Partitioning of the Picture into Subpictures

A subpicture may be a rectangular partition of a picture. A subpicturecan be the whole picture or a part of the picture. A subpicture ispartitioning of a picture in such a way that each subpicture isindependently decodable from other subpictures of the entire videosequence. In VVC draft 8, when subpic_treated_as_pic_flag[i] indicationis true (e.g. a value of subpic_treated_as_pic_flag[i] is 1) forsubpicture i, that subpicture i is independently decodable from othersubpictures of the entire video sequence.

The difference between the subpicture and tiles or slices is that,subpictures create an independently decodable video sequence. For tilesand slices, independent decoding is performed in a single picture of avideo sequence.

In VVC draft 8, a subpicture comprises one or more slices thatcollectively cover a rectangular region of a picture. Consequently, eachsubpicture boundary is always a slice boundary, and each verticalsubpicture boundary is always a vertical tile boundary.

FIG. 10 provides an example of tiles, slices and subpictures.

In one example as shown in FIG. 8, a picture is partitioned into 216CTUs, 4 tiles, 4 slices and 3 subpictures. A value ofsps_num_subpics_minus1 is 2, and the position-related syntax elementshave the following values:

For subpicture 0,

-   -   subpic_ctu_top_left_x[0] is not signaled but inferred as 0;    -   subpic_ctu_top_left_y[0] is not signaled but inferred as 0;    -   subpic_width_minus1[0] value is 8;    -   subpic_height_minus1[0] value is 11.

For subpicture 1,

-   -   subpic_ctu_top_left_x[1] value is 9;    -   subpic_ctu_top_left_y[1] value is 0;    -   subpic_width_minus1[1] value is 8;    -   subpic_height_minus1[1] value is 5.

For subpicture 2,

-   -   subpic_ctu_top_left_x[2] value is 9;    -   subpic_ctu_top_left_y[2] value is 6;    -   subpic_width_minus1[2] is not signaled but inferred as 8;    -   subpic_height_minus1[2] is not signaled but inferred as 5.

Signaling of Decoded Picture Buffer (DPB) Information.

Decoded Picture Buffer

Decoded Picture Buffer (DPB) is a buffer which is used to store thedecoded picture for reference, for example, as a reference picture forinter prediction. In an example disclosed in VVC draft (e.g. ITUJVET-Q2001-v13), the related syntax elements of parameters for DBP insequence parameter set (SPS) are highlighted.

TABLE 6 Decoded picture related syntax elements in SPS sps_poc_msb_flagu(1) if( sps_poc msb_flag )  poc_msb_len_minus1 ue(v)num_extra_ph_bits_bytes u(2)  extra_ph_bits_struct(num_extra_ph_bits_bytes ) num_extra_sh_bits_bytes u(2) extra_sh_bits_struct( num_extra_sh_bits_bytes ) if(sps_max_sublayers_minus1 > 0)  sps_sublayer_dpb_params_flag u(1) if(sps_ptl_dpb_hrd_params_present_flag )  dpb_parameters(sps_max_sublayers_minus1, sps_sublayer_dpb_params_flag )long_term_ref_pics_flag u(1)

sps_max_sublayers_minus1 plus 1 specifies the maximum number of temporalsublayers that may be present in each CLVS referring to the SPS. Thevalue of sps_max_sublayers_minus1 shall be in the range of 0 tovps_max_sublayers_minus1, inclusive.

sps_sublayer_dpb_params_flag is used to control the presence ofmax_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], andmax_latency_increase_plus1[i] syntax elements in the dpb_parameters( )syntax structure in the SPS. When not present, the value ofsps_sub_dpb_params_info_present_flag is inferred to be equal to 0.

sps_ptl_dpb_hrd_params_present_flag equal to 1 specifies that aprofile_tier_level( ) syntax structure and a dpb_parameters( ) syntaxstructure are present in the SPS, and a general_hrd_parameters( ) syntaxstructure and an ols_hrd_parameters( ) syntax structure may also bepresent in the SPS. sps_ptl_dpb_hrd_params_present_flag equal to 0specifies that none of these four syntax structures is present in theSPS. The value of sps_ptl_dpb_hrd_params_present_flag shall be equal tovps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]].

A syntax element sps_max_sublayers_minus1 indicates a number ofavailable temporal sublayers. When a number of available temporalsublayers is larger than 1 (e.g. a value of syntax elementsps_max_sublayers_minus1 is greater than 0), a value of the syntaxelement sps_sublayer_dpb_params_flag is signaled in a bitstream. Becausethe syntax element sps_sublayer_dpb_params_flag mandates whether tosignal decode picture information for each available sublayer (when itsvalue is equal to 1) or to signal just for the highest temporal sublayer(when its value is equal to 0). When a value ofsps_sublayer_dpb_params_flag is not present, e.g. there is only onetemporal sublayer (a value of sps_max_sublayers_minus1==0), the value ofsps_max_sublayers_minus1 is inferred as 0.

In some examples, a value of syntax elementsps_ptl_dpb_hrd_params_present_flag indicates whether a signalingstructure dpb_parameter( ) is signaled in SPS or not. When a value ofsyntax element sps_ptl_dpb_hrd_params_present_flag is equal to 1, thesignaled date structure dpb_parameter( ) is invoked, with the number ofavailable temporal sublayers minus 1 (sps_max_sublayers_minus1) and theflag sps_sublayer_dpb_params_flag as the first and second parameter,respectively.

In an example, the signaling structure of dpb_parameter( ) in VVC draft(e.g. ITU JVET-Q2001-v13) is defined as follows:

TABLE 7 definition of dpb_parameters dpb_parameters( maxSubLayersMinus1,subLayerInfoFlag ) { Descriptor  for( i = ( subLayerInfoFlag ? 0 :maxSubLayersMinus1 );    i <= maxSubLayersMinus1; i++ ) {  max_dec_pic_buffering_minus1[ i ] ue(v)   max_num_reorder_pics[ i ]ue(v)   max_latency_increase_plus1[ i ] ue(v)  } }

The dpb_parameters( ) syntax structure provides information of DPB size,maximum picture reorder number, and maximum latency for one or moreOLSs.

(output layer set (OLS): A set of layers consisting of a specified setof layers, where one or more layers in the set of layers are specifiedto be output layers).

When a dpb_parameters( ) syntax structure is included in a VPS, the OLSsto which the dpb_parameters( ) syntax structure applies are specified bythe VPS. When a dpb_parameters( ) syntax structure is included in anSPS, it applies to the OLS that includes only the layer that is thelowest layer among the layers that refer to the SPS, and this lowestlayer is an independent layer.

max_dec_pic_buffering_minus1[i] plus 1 specifies the maximum requiredsize of the DPB in units of picture storage buffers when Htid is equalto i. The value of max_dec_pic_buffering_minus1[i] shall be in the rangeof 0 to MaxDpbSize−1, inclusive, where MaxDpbSize is as specified inclause A.4.2. When i is greater than 0, max_dec_pic_buffering_minus1[i]shall be greater than or equal to max_dec_pic_buffering_minus1[i−1].When max_dec_pic_buffering_minus1[i] is not present for i in the rangeof 0 to maxSubLayersMinus1−1, inclusive, due to subLayerInfoFlag beingequal to 0, it is inferred to be equal tomax_dec_pic_buffering_minus1[maxSubLayersMinus1].

max_num_reorder_pics[i] specifies the maximum allowed number of picturesof the OLS that can precede any picture in the OLS in decoding order andfollow that picture in output order when Htid is equal to i. The valueof max_num_reorder_pics[i] shall be in the range of 0 tomax_dec_pic_buffering_minus1[i], inclusive. When i is greater than 0,max_num_reorder_pics[i] shall be greater than or equal tomax_num_reorder_pics[i−1]. When max_num_reorder_pics[i] is not presentfor i in the range of 0 to maxSubLayersMinus1−1, inclusive, due tosubLayerInfoFlag being equal to 0, it is inferred to be equal tomax_num_reorder_pics[maxSubLayersMinus1].

max_latency_increase_plus1[i] not equal to 0 is used to compute thevalue of MaxLatencyPictures[i], which specifies the maximum number ofpictures in the OLS that can precede any picture in the OLS in outputorder and follow that picture in decoding order when Htid is equal to i.

When max_latency_increase_plus1[i] is not equal to 0, the value ofMaxLatencyPictures[i] is specified as follows:

MaxLatencyPictures[i]=max_num_reorder_pics[i]+max_latency_increase_plus1[i]−1  (7-111)

When max_latency_increase_plus1[i] is equal to 0, no corresponding limitis expressed.

The value of max_latency_increase_plus1[i] shall be in the range of 0 to2³²-2, inclusive. When max_latency_increase_plus1[i] is not present fori in the range of 0 to maxSubLayersMinus1−1, inclusive, due tosubLayerInfoFlag being equal to 0, it is inferred to be equal tomax_latency_increase_plus1[maxSubLayersMinus1].

The dpb_parameters signaling structure either signals one sublayer'sdecoded picture buffer information or each sublayer's decoded pictureinformation, controlled by the value of subLayerInfoFlag. When a valueof subLayerInfoFlag is 0, the decoded picture buffer information of thehighest sublayer among the available temporal sublayers is signaled(i=maxSubLayersMinus1). When a value of subLayerInfoFlag is 1, thedecoded picture buffer information of each sublayer among the availabletemporal sublayers is signaled (a value of i ranges from 0 tomaxSubLayersMinus1, inclusive).

In some examples, the syntax element sps_sublayer_dpb_params_flag isused only as the second parameter of the dpb_parameters.

Embodiment 10

According to the tenth embodiment, a value of the syntax elementsps_sublayer_dpb_params_flag is coded in a bitstream, based on a valueof the syntax element sps_ptl_dpb_hrd_params_present_flag as follows:

TABLE 8 Syntax Elements in SPS sps_poc_msb_flag u(1) if(sps_poc_msb_flag )  poc_msb_len_minus1 ue(v) num_extra_ph_bits_bytesu(2)  extra_ph_bits_struct( num_extra_ph_bits_bytes )num_extra_sh_bits_bytes u(2)  extra_sh_bits_struct(num_extra_sh_bits_bytes ) if( sps_max_sublayers_minus1 > 0 &&sps_ptl_dpb_hrd_params_present_flag)  sps_sublayer_dpb_params_flag u(1)if( sps_ptl_dpb_hrd_params_present_flag )  dpb_parameters(sps_max_sublayers_minus1, sps_sublayer_dpb_params_flag )long_term_ref_pics_flag u(1)

In this embodiment, when a value of sps_max_sublayers_minus1 is largerthan 0 and a value of sps_ptl_dpb_hrd_params_present_flag is equal to 0,a value of syntax element sps_sublayer_dpb_params_flag is not need to becoded in a bitstream.

Embodiment 11

According to the eleventh embodiment, a value of syntax elementsps_sublayer_dpb_params_flag is coded in a bitstream, based on a valueof the syntax element sps_ptl_dpb_hrd_params_present_flag as follows:

TABLE 9 Syntax Elements in PPS sps_poc_msb_flag u(1) if( sps_pocmsb_flag) flag )  poc_msb_len_minus1 ue(v) num_extra_ph_bits_bytes u(2) extra_ph_bits_struct( num_extra_ph_bits_bytes ) num_extra_sh_bits_bytesu(2)  extra_sh_bits_struct( num_extra_sh_bits_bytes )if(sps_ptl_dpb_hrd_params_present_flag){  if (sps_max_sublayers_minus1 >0)   sps_sublayer_dpb_params_flag u(1)  dpb_parameters( spsmax_sublayers_minus1, sps_sublayer_dpb_params_flag ) }long_term_ref_pics_flag u(1)

In this embodiment, when a value of sps_max_sublayers_minus1 is largerthan 0 and a value of sps_ptl_dpb_hrd_params_present_flag is equal to 0,a value of syntax element sps_sublayer_dpb_params_flag is not need to becoded in a bitstream. Furthermore, the syntax elements are restructuredwith a clearer design. The syntax elementsps_ptl_dpb_hrd_params_present_flag is leveled up to mandate thesignaling of both syntax element sps_sublayer_dpb_params_flag and thesignaling structure dpb_parameters( ).

Embodiment 12

According to the twelfth embodiment, a value of the syntax elementsps_sublayer_dpb_params_flag is coded in a bitstream, based on a valueof the syntax element sps_ptl_dpb_hrd_params_present_flag as follows:

TABLE 10 Syntax Elements in PPS sps_poc_msb_flag u(1) if(sps_poc_msb_flag )  poc_msb_len_minus1 ue(v) num_extra_ph_bits_bytesu(2)  extra_ph_bits_struct( num_extra_ph_bits_bytes )num_extra_sh_bits_bytes u(2)  extra_sh_bits_strucht(num_extra_sh_bits_bytes ) if(sps_ptl_dpb_hrd_params_present_flag){  if(sps_max_sublayers_minus1 > 0)   sps_sublayer_dpb_params_flag u(1) firstSubLayer = sps_sublayer_dpb_params_flag ? 0:sps_max_sublayers_minus1  dpb_parameters( firstSubLayer,sps_max_sublayers_minus1) } long_term_ref_pics_flag u(1)

Correspondingly, the signaling structure of dpb_parameters is modifiedas follows:

dpb_parameters( firstSubLayer, maxSubLayersMinus1) { Descriptor  for( i= firstSubLayer; i <= maxSubLayersMinus1; i++ ) {  max_dec_pic_buffering_minus1[ i ] ue(v)   max_num_reorder_pics[ i ]ue(v)   max_latency_increase_plus1[ i ] ue(v)  } }

In this embodiment, when a value of sps_max_sublayers_minus1I is largerthan 0 and a value of sps_ptl_dpb_hrd_params_present_flag is equal to 0,a value of syntax element sps_sublayer_dpb_params_flag is not need to becoded in a bitstream. Compared to embodiment 11, the signaling structureof dpb_parameter( ) is signaled from the first sublayer to the highestsublayer, indicates by the parameter firstSubLayer andmaxSubLayersMinus1, respectively. The selection of first sublayer is putout of dpb_parameter( ). The semantics of sps_sublayer_dpb_params_flagis clearer in this way.

In an example, as disclosed in VVC draft (e.g. ITU JVET-Q2001-v13),there are two modes for slice, raster scan slice mode and rectangleslice mode. However, according to current definition, a slice can beeither in raster scan mode or in rectangle mode.

The definition of slices is described as follows:

A slice consists of an integer number of complete tiles or an integernumber of consecutive complete CTU rows within a tile of a picture.Consequently, each vertical slice boundary is always also a verticaltile boundary. It is possible that a horizontal boundary of a slice isnot a tile boundary but consists of horizontal CTU boundaries within atile; this occurs when a tile is split into multiple rectangular slices,each of which consists of an integer number of consecutive complete CTUrows within the tile.

Two modes of slices are supported, namely the raster-scan slice mode andthe rectangular slice mode. In the raster-scan slice mode, a slicecontains a sequence of complete tiles in a tile raster scan of apicture. In the rectangular slice mode, a slice contains either a numberof complete tiles that collectively form a rectangular region of thepicture or a number of consecutive complete CTU rows of one tile thatcollectively form a rectangular region of the picture. Tiles within arectangular slice are scanned in tile raster scan order within therectangular region corresponding to that slice.

The only constraint for raster-scan slice is it “contains a sequence ofcomplete tiles in a tile raster scan of a picture”. As shown in FIG. 12,for example, there are only two tiles and one slice in a picture. Thisslice can be either in raster scan slice mode or rectangle slice mode.This could cause confusion for the two modes of the slice.

Embodiment 13

It is suggested to further restrict the definition of raster scan sliceas follows:

In the raster-scan slice mode, a slice contains a sequence of completetiles in a tile raster scan of a picture and this picture contains atleast one slice forming a non-rectangle shape.

For example, with this definition of the raster scan slice, a picture asshown in FIG. 13 is a raster scan slice, but a picture as shown in FIG.12 can only use rectangle slice mode.

Correspondingly, the signaling for tile structure is modified.

In one example, the signaling of tile information is as follows in PPS:

if( !no_pic_partition_flag) {  pps_log2_ctu_size_minus5 u(2) num_exp_tile_columns_minus1 ue(v)  num_exp_tile_rows_minus1 ue(v)  for(i = 0; i <= num_exp_tile_columns_minus1; i++ )  tile_column_width_minus1[ i ] ue(v)  for( i = 0; i <=num_exp_tile_rows_minus1; i++ )   tile_row_height_minus1[ i ] ue(v)  if(NumTilesInPic > 1)   rect_slice_flag u(1)  if( rect_slice_flag )  single_slice_per_subpic_flag u(1)no_pic_partition_flag equal to 1 specifies that no picture partitioningis applied to each picture referring to the PPS. no_pic_partition_flagequal to 0 specifies each picture referring to the PPS may bepartitioned into more than one tile or slice.It is a requirement of bitstream conformance that the value ofno_pic_partition_flag shall be the same for all PPSs that are referredto by coded pictures within a CLVS.

It is a requirement of bitstream conformance that the value ofno_pic_partition_flag shall not be equal to 1 when the value ofsps_num_subpics_minus1+1 is greater than 1.

pps_log 2_ctu_size_minus5 plus 5 specifies the luma coding tree blocksize of each CTU. pps_log 2_ctu_size_minus5 shall be equal to sps_log2_ctu_size_minus5.

num_exp_tile_columns_minus1 plus 1 specifies the number of explicitlyprovided tile column widths. The value of num_exp_tile_columns_minus1shall be in the range of 0 to PicWidthInCtbsY−1, inclusive. Whenno_pic_partition_flag is equal to 1, the value ofnum_exp_tile_columns_minus1 is inferred to be equal to 0.

num_exp_tile_rows_minus1 plus 1 specifies the number of explicitlyprovided tile row heights. The value of num_exp_tile_rows_minus1 shallbe in the range of 0 to PicHeightInCtbsY−1, inclusive. Whenno_pic_partition_flag is equal to 1, the value of num_tile_rows_minus1is inferred to be equal to 0.

tile_column_width_minus1[i] plus 1 specifies the width of the i-th tilecolumn in units of CTBs for i in the range of 0 to numexp_tile_columns_minus1−1, inclusive.tile_column_width_minus1[num_exp_tile_columns_minus1] is used to derivethe width of the tile columns with index greater than or equal tonum_exp_tile_columns_minus1 as specified in clause 6.5.1. The value oftile_column_width_minus1[i] shall be in the range of 0 toPicWidthInCtbsY−1, inclusive. When not present, the value oftile_column_width_minus1[0] is inferred to be equal toPicWidthInCtbsY−1.

tile_row_height_minus1[i] plus 1 specifies the height of the i-th tilerow in units of CTBs for i in the range of 0 tonum_exp_tile_rows_minus1−1, inclusive.tile_row_height_minus11[num_exp_tile_rows_minus1] is used to derive theheight of the tile rows with index greater than or equal tonum_exp_tile_rows_minus1 as specified in clause 6.5.1. The value oftile_row_height_minus1[i] shall be in the range of 0 toPicHeightInCtbsY−1, inclusive. When not present, the value oftile_row_height_minus1[0] is inferred to be equal to PicHeightInCtbsY−1.

rect_slice_flag equal to 0 specifies that tiles within each slice are inraster scan order and the slice information is not signalled in PPS.rect_slice_flag equal to 1 specifies that tiles within each slice covera rectangular region of the picture and the slice information issignalled in the PPS. When not present, rect_slice_flag is inferred tobe equal to 1. When subpic_info_present_flag is equal to 1, the value ofrect_slice_flag shall be equal to 1.

single_slice_per_subpic_flag equal to 1 specifies that each subpictureconsists of one and only one rectangular slice.single_slice_per_subpic_flag equal to 0 specifies that each subpicturemay consist of one or more rectangular slices. Whensingle_slice_per_subpic_flag is equal to 1, num_slices_in_pic_minus1 isinferred to be equal to sps_num_subpics_minus1. When not present, thevalue of single_slice_per_subpic_flag is inferred to be equal to 0. [Ed.(GJS): Consider renaming this flag or clarifying in another manner toavoid an interpretation that this flag is only relevant when there aremore than one subpictures in each picture.]

When a number of tile in picture is larger than 1, a flagrect_slice_flag is parsed from a bitstream, a value of rect_slice_flagindicating whether a rectangle slice mode (when the value is equal to 1)is used for a picture or a raster scan slice mode (when the value isequal to 0) is used for the picture.

Correspondingly, in slice header

slice_header( ) { Descriptor  picture_header_in_slice_header_flag u(1) if( picture_header_in_slice_header_flag )   picture_header_structure( ) if( subpic_info_present_flag )   slice_subpic_id u(v)  if( (rect_slice_flag && NumSlicesInSubpic[ CurrSubpicIdx ] > 1) | |    (!rect_slice_flag && NumTilesInPic > 1 ) )   slice_address u(v)  for( i =0; i < NumExtraPhBits; i++ )   sh_extra_bit[ i ] u(1)  if(!rect_slice_flag && NumTilesInPic > 1 )   num_tiles_in_slice_minus1ue(v)

picture_header_in_slice_header_flag equal to 1 specifies that the PHsyntax structure is present in the slice header.picture_header_in_slice_header_flag equal to 0 specifies that the PHsyntax structure is not present in the slice header.

It is a requirement of bitstream conformance that the value ofpicture_header_in_slice_header_flag shall be the same in all codedslices in a CLVS.

When picture_header_in_slice_header_flag is equal to 1 for a codedslice, it is a requirement of bitstream conformance that no VCL NAL unitwith nal_unit_type equal to PH_NUT shall be present in the CLVS.

When picture_header_in_slice_header_flag is equal to 0, all coded slicesin the current picture shall have picture_header_in_slice_header_flag isequal to 0, and the current PU shall have a PH NAL unit.

slice_subpic_id specifies the subpicture ID of the subpicture thatcontains the slice. If slice_subpic_id is present, the value of thevariable CurrSubpicIdx is derived to be such thatSubpicIdVal[CurrSubpicIdx] is equal to slice_subpic_id. Otherwise(slice_subpic_id is not present), CurrSubpicIdx is derived to be equalto 0. The length of slice_subpic_id is sps_subpic_id_len_minus1+1 bits.

slice_address specifies the slice address of the slice. When notpresent, the value of slice_address is inferred to be equal to 0. Whenrect_slice_flag is equal to 1 and NumSlicesInSubpic[CurrSubpicIdx] isequal to 1, the value of slice_address is inferred to be equal to 0.

If rect_slice_flag is equal to 0, the following applies:

-   -   The slice address is the raster scan tile index.    -   The length of slice_address is Ceil(Log 2 (NumTilesInPic)) bits.    -   The value of slice_address shall be in the range of 0 to        NumTilesInPic−1, inclusive.

Otherwise (rect_slice_flag is equal to 1), the following applies:

-   -   The slice address is the subpicture-level slice index of the        slice.    -   The length of slice_address is Ceil(Log        2(NumSlicesInSubpic[CurrSubpicIdx])) bits.    -   The value of slice_address shall be in the range of 0 to        NumSlicesInSubpic[CurrSubpicIdx]−1, inclusive.

It is a requirement of bitstream conformance that the followingconstraints apply:

-   -   If rect_slice_flag is equal to 0 or subpic_info_present_flag is        equal to 0, the value of slice_address shall not be equal to the        value of slice_address of any other coded slice NAL unit of the        same coded picture.    -   Otherwise, the pair of slice_subpic_id and slice_address values        shall not be equal to the pair of slice_subpic_id and        slice_address values of any other coded slice NAL unit of the        same coded picture.    -   The shapes of the slices of a picture shall be such that each        CTU, when decoded, shall have its entire left boundary and        entire top boundary consisting of a picture boundary or        consisting of boundaries of previously decoded CTU(s).

sh_extra_bit[i] may be equal to 1 or 0. Decoders conforming to thisversion of this Specification shall ignore the value of sh_extra_bit[i].Its value does not affect decoder conformance to profiles specified inthis version of specification.

num_tiles_in_slice_minus1 plus 1, when present, specifies the number oftiles in the slice. The value of num_tiles_in_slice_minus1 shall be inthe range of 0 to NumTilesInPic−1, inclusive.

It is suggested to modify the above signaling mechanism as follows inPPS and slice header:

 if( !no_pic_partition_flag) {   pps_log2_ctu_size_minus5 u(2)  num_exp_tile_columns_minus1 ue(v)   num_exp_tile_rows_minus1 ue(v)  for( i = 0; i <= num_exp_tile_columns_minus1; i++ )   tile_column_width_minus1[ i ] ue(v)   for( i = 0; i <=num_exp_tile_rows_minus1; i++ )    tile_row_height_minus1[ i ] ue(v)  if( NumTilesInPic > 3 )    rect_slice_flag u(1)   if( rect_slice_flag)    single_slice_per_subpic_flag u(1) slice header( ) { Descriptor picture_header_in_slice_header_flag u(1)  if(picture_header_in_slice_header_flag )   picture_header_structure( )  if(subpic_info_present_flag )   slice_subpic_id u(v)  if( ( rect_slice_flag&& NumSlicesInSubpic[ CurrSubpicIdx ] > 1 ) | |    ( !rect_slice_flag &&NumTilesInPic > 3 ) )   slice_address u(v)  for( i = 0; i <NumExtraPhBits; i++ )   sh_extra_bit[ i ] u(1)  if( !rect_slice_flag &&NumTilesInPic > 3 )   num_tiles_in_slice_minus1 ue(v)

Particularly, the following embodiments are also provided herein (in newenumeration).

Embodiment 1. A method of coding implemented by a decoding device or anencoding device, the method comprising:

obtaining a bitstream, a sequence parameter set, SPS, is coded in thebitstream;

obtaining a value of a first syntax element sps_max_sublayers_minus1according to the bitstream, wherein the value of the first syntaxelement sps_max_sublayers_minus1I is used to indicate the maximum numberof temporal sublayers that present in a coded layer video sequence,CLVS, referring to the SPS;

obtaining a value of a second syntax elementsps_ptl_dpb_hrd_params_present_flag according to the bitstream, whereinthe value of the second syntax elementsps_ptl_dpb_hrd_params_present_flag is used to indicate whether adecoded picture buffer, DPB, parameters syntax structure (e.g.dpb_prameters) is present in the SPS;

parsing a value of a third syntax element sps_sublayer_dpb_params_flagfrom the bitstream, when the value of the first syntax elementsps_max_sublayers_minus1 is greater than a first default value (e.g. thefirst default value is equal to 0) and when the value of the secondsyntax element sps_ptl_dpb_hrd_params_present_flag is equal to a seconddefault value (e.g. the second default value is equal to 1), wherein thevalue of the third syntax element sps_sublayer_dpb_params_flag is usedto control presence of a syntax element (e.g.max_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], and/ormax_latency_increase_plus1[i] for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0) in the DPB parameters syntax structure (e.g.dpb_prameters) in the SPS.

Embodiment 2. The method of embodiment 1, wherein the method furthercomprises:

setting the value of the third syntax elementsps_sublayer_dpb_params_flag to a third default value (e.g. the thirddefault value is equal to 0 or 1), when the value of the first syntaxelement sps_max_sublayers_minus1 is smaller than or equal to the firstdefault value or when the value of the second syntax elementsps_ptl_dpb_hrd_params_present_flag is not equal to the second defaultvalue.

Embodiment 3. The method of embodiment 1 or 2, wherein the value of thethird syntax element sps_sublayer_dpb_params_flag is coded in the SPS.

Embodiment 4. A method of coding implemented by a decoding device or anencoding device, the method comprising:

obtaining a bitstream, a sequence parameter set, SPS, is coded in thebitstream;

obtaining a value of a first syntax element sps_max_sublayers_minus1according to the bitstream, wherein the value of the first syntaxelement sps_max_sublayers_minus1 is used to specifies the maximum numberof temporal sublayers that present in a coded layer video sequence,CLVS, referring to the SPS;

obtaining a value of a second syntax elementsps_ptl_dpb_hrd_params_present_flag according to the bitstream, whereinthe value of the second syntax elementsps_ptl_dpb_hrd_params_present_flag is used to specify whether a decodedpicture buffer, DPB, parameters syntax structure (e.g. dpb_prameters) ispresent in the SPS;

determining whether the value of the second syntax elementsps_ptl_dpb_hrd_params_present_flag is equal to a second default value(e.g. the second default value is equal to 1);

determining whether the value of the first syntax elementsps_max_sublayers_minus1 is greater than a first default value (e.g. thefirst default value is equal to 0), when it's determined that the valueof the second syntax element sps_ptl_dpb_hrd_params_present_flag isequal to the second default value;

parsing a value of a third syntax element sps_sublayer_dpb_params_flagfrom the bitstream, when it's determined that the value of the firstsyntax element sps_max_sublayers_minus1 is greater than the firstdefault value (e.g. the first default value is equal to 0), wherein thevalue of the third syntax element sps_sublayer_dpb_params_flag is usedto control presence of a syntax element (e.g.max_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], and/ormax_latency_increase_plus1[i] for i in range from 0 tosps_max_sublayers_minus1−1, inclusive, when sps_max_sublayers_minus1 islarger than 0) in the DPB parameters syntax structure (e.g.dpb_prameters) in the SPS.

Embodiment 5. The method of embodiment 4, wherein the method furthercomprises:

setting the value of the third syntax elementsps_sublayer_dpb_params_flag to a third default value (e.g. the thirddefault value is equal to 0 or 1), when it's determined that the valueof the first syntax element sps_max_sublayers_minus1 is smaller than orequal to the first default value or when it's determined that the valueof the second syntax element sps_ptl_dpb_hrd_params_present_flag is notequal to the second default value.

Embodiment 6. The method of embodiment 4 or 5, wherein the value of thethird syntax element sps_sublayer_dpb_params_flag is coded in the SPS(in other examples, the value of the third syntax elementsps_sublayer_dpb_params_flag is coded in a picture parameter set, PPS orthe value of the third syntax element sps_sublayer_dpb_params_flag iscoded in a video parameter set, VPS).

Embodiment 7. The method of any one of embodiments 1 to 6, wherein thevalue of the first syntax element is coded in a picture parameter set,PPS or the value of the first syntax element is coded in a videoparameter set, VPS (in another example, the value of the second syntaxelement is coded in a picture parameter set, PPS or the value of thesecond syntax element is coded in a video parameter set, VPS).

Embodiment 8. The method of any one of embodiments 1 to 7, wherein whensps_max_sublayers_minus1 is equal to 0, max_dec_pic_buffering_minus1[0],max_num_reorder_pics[0], and max_latency_increase_plus1[0] is alwayssignaled for the only sublayer referred to the SPS.

Embodiment 9. A method of coding implemented by a decoding device or anencoding device, the method comprising:

determining an indirect reference layer with index j of a layer withindex i, only from at least one layer with index lower than i;

when inter-layer prediction is enabled for current picture, obtain itsreference picture in the indirect reference layer with index j,

predicting a current picture using the reference picture from theindirect reference layer with index j.

Embodiment 10. The method of embodiment 9, wherein the determining theindirect reference layer of the layer with index i comprises:determining that there is a layer with index k, only among at least onelayer with index lower than i and higher than j, is the direct referenceof the layer with index i, wherein the indirect reference layer withindex j is a reference layer of the direct reference layer with index k.

Embodiment 11. The method of embodiment 9, wherein the determining theindirect direct reference layer of the layer with index i comprises:determining that there is a layer with index k, only among at least onelayer with index lower than i, is the direct reference of the layer withindex i, wherein the indirect reference layer with index j is areference layer of the direct reference layer with index k.

Embodiment 12. A method of coding implemented by a decoding device or anencoding device, the method comprising:

determining an indirect reference layer with index j of a layer withindex i, when it is determined that there is a layer with index k, onlyamong at least one layer with index lower than i and higher than j, isthe direct reference layer of the layer with index i, and wherein thelayer with index j is a reference layer of the direct reference layerwith index k.

when inter-layer prediction is enabled for current picture, obtain itsreference picture in the indirect reference layer with index j,

predicting a current picture using the reference picture from theindirect reference layer with index j.

Embodiment 13. A method of coding implemented by a decoding device or anencoding device, the method comprising:

obtaining a bitstream, a picture parameter set, PPS, is coded in thebitstream;

obtaining a number of tile columns NumTileColumns for a current picture(e.g. the current picture contains at least one slice forming anon-rectangle shape) according to the bitstream;

obtaining a number of tile rows NumTileRows for the current pictureaccording to the bistream;

obtaining a value of variable NumTilesInPic according to the number oftile columns NumTileColumns and the number of tile rows NumTileRows;

parsing a value of a syntax element rect_slice_flag from the bitstream,when the value of variable NumTilesInPic is greater than a preset value(e.g. the preset value is 3), wherein the value of the syntax elementrect_slice_flag is used to specify whether slice information is signaledin the PPS.

Embodiment 14. The method of embodiment 13, wherein the method furthercomprise:

setting the value of the syntax element rect_slice_flag to a fourthdefault value (e.g. the fourth default value is equal toT), when thevalue of variable NumTilesInPic is smaller than or equal to the presetvalue.

Embodiment 15. The method of embodiment 13 or 14, wherein the value ofvariable NumTilesInPic is equal to NumTileColumns*NumTileRows.

Embodiment 16. The method of any one of embodiments 13 to 15, whereinthe method further comprises:

parsing a value of a slice address slice_address of a current slice fromthe bitstream, when value of the syntax element rect_slice_flag is equalto a fifth default value (e.g. the fifth default value is equal to 0)and when the value of variable NumTilesInPic is greater than the presetvalue, wherein the current slice is comprised in the current picture.

Embodiment 17. The method of embodiment 16, wherein the value of theslice address is coded in a slice header for the current slice.

Embodiment 18. The method of any one of embodiments 13 to 17, whereinthe method further comprises:

obtaining a number of tiles num_tiles_in_slice_minus1 comprised in thecurrent slice, when the value of the syntax element rect_slice_flag isequal to the fifth default value and when the value of variableNumTilesInPic is greater than the preset value.

Embodiment 19. The method of embodiment 18, wherein the number of tilenum_tiles_in slice minus1 is coded in a slice header for the currentslice.

Embodiment 20. A decoder comprising processing circuitry for carryingout the method according to any one of embodiments 1 to 19.

21. A computer program product comprising program code for performingthe method according to any one of the embodiments 1 to 19 when executedon a computer or a processor.

22. A decoder, comprising:

one or more processors; and

a non-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures thedecoder to carry out the method according to any one of the embodiments1 to 19.

23. A non-transitory computer-readable medium carrying a program codewhich, when executed by a computer device, causes the computer device toperform the method of any one of the embodiments 1 to 19.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 8 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and optionallyincludes display 3126. The capture device 3102 communicates with theterminal device 3106 over communication link 3104. The communicationlink may include the communication channel 13 described above. Thecommunication link 3104 includes but not limited to WIFI, Ethernet,Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, orthe like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 9 is a diagram showing a structure of an example of the terminaldevice 3106. After the terminal device 3106 receives stream from thecapture device 3102, the protocol proceeding unit 3202 analyzes thetransmission protocol of the stream. The protocol includes but notlimited to Real Time Streaming Protocol (RTSP), Hyper Text TransferProtocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH,Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP),or any kind of combination thereof, or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and optionally subtitle are generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. 9) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer (not shown in FIG. 9) before feedingit to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

The present embodiment of the disclosure is not limited to theabove-mentioned system, and either the picture encoding device or thepicture decoding device in the above-mentioned embodiments can beincorporated into other system, for example, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   -   + Addition    -   − Subtraction (as a two-argument operator) or negation (as a        unary prefix operator)    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   + Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

Used to denote division in mathematical equations where no truncation orrounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

The summation of f(i) with i taking all integer values from x up to andincluding y.

-   -   x % y Modulus. Remainder of x divided by y, defined only for        integers x and y with x>=0 and y>0.

Logical Operators

The following logical operators are defined as follows:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x ? y: z If x is TRUE or not equal to 0, evaluates to the value        of y; otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   -   > Greater than    -   >= Greater than or equal to    -   < Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   -   & Bit-wise “and”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   | Bit-wise “or”. When operating on integer arguments, operates        on a two's complement representation of the integer value. When        operating on a binary argument that contains fewer bits than        another argument, the shorter argument is extended by adding        more significant bits equal to 0.    -   {circumflex over ( )} Bit-wise “exclusive or”. When operating on        integer arguments, operates on a two's complement representation        of the integer value. When operating on a binary argument that        contains fewer bits than another argument, the shorter argument        is extended by adding more significant bits equal to 0.    -   x>>y Arithmetic right shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        most significant bits (MSBs) as a result of the right shift have        a value equal to the MSB of x prior to the shift operation.    -   x<<y Arithmetic left shift of a two's complement integer        representation of x by y binary digits. This function is defined        only for non-negative integer values of y. Bits shifted into the        least significant bits (LSBs) as a result of the left shift have        a value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

-   -   = Assignment operator    -   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an        array index, evaluates to the value of the variable prior to the        increment operation.    -   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an        array index, evaluates to the value of the variable prior to the        decrement operation.    -   += Increment by amount specified, i.e., x+=3 is equivalent to        x=x+3, and x+=(−3) is equivalent to x=x+(−3).    -   −= Decrement by amount specified, i.e., x−=3 is equivalent to        x=x−3, and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   -   x=y . . . z x takes on integer values starting from y to z,        inclusive, with x, y, and z being integer numbers and z being        greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}{x;} & {x>=0} \\{{- x};} & {x < 0}\end{matrix} \right.$

-   -   Asin(x) the trigonometric inverse sine function, operating on an        argument x that is in the range of −1.0 to 1.0, inclusive, with        an output value in the range of −π+2 to π+2, inclusive, in units        of radians    -   Atan(x) the trigonometric inverse tangent function, operating on        an argument x, with an output value in the range of −π÷2 to π÷2,        inclusive, in units of radians

${A\tan 2\left( {y,x} \right)} = \left\{ \begin{matrix}{{{A\;{\tan\ \left( \frac{y}{x} \right)}};}\ } & {x > 0} \\{{{{A\;{\tan\ \left( \frac{y}{x} \right)}} + \pi};}\ } & {{{{{x < 0}\ \&}\&}\ y}>=0} \\{{{A\;{\tan\ \left( \frac{y}{x} \right)}} - \pi};} & {\ {{{{{x < 0}\ \&}\&}\ y} < 0}} \\{{{+ \frac{\pi}{2}};}\ } & {{x=={{{{0\ \&}\&}\ y} >}} = 0} \\{{{- \ \frac{\pi}{2}};}\ } & {otherwise}\end{matrix} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.    -   Clip1_(Y)(x)=Clip3(0, (1<<BitDepth_(Y))−1, x)    -   Clip1_(C)(x)=Clip3(0, (1<<BitDepth_(C))−1, x)

${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{x;} & {z < x} \\{y;} & {z > y} \\{z;} & {otherwise}\end{matrix} \right.$

-   -   Cos(x) the trigonometric cosine function operating on an        argument x in units of radians.    -   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{{{c + d};}\ } & {{b - a}\ >={d/2}} \\{{{c - d};}\ } & {{a - b}\  > {d/2}} \\{c;} & {otherwise}\end{matrix} \right.$

-   -   Ln(x) the natural logarithm of x (the base-e logarithm, where e        is the natural logarithm base constant 2.718 281 828 . . . ).    -   Log 2(x) the base-2 logarithm of x.    -   Log 10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ {{\begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix}{{Round}(x)}} = {{{{Sign}(x)}*{{Floor}\left( {{{Abs}(x)} + {0.5}} \right)}{{Sign}(x)}} = \left\{ \begin{matrix}{1;} & {x > 0} \\{0;} & {x==0} \\{{- 1};} & {x < 0}\end{matrix} \right.}} \right.} \right.$

Sin(x) the trigonometric sine function operating on an argument x inunits of radians

-   -   Sqrt(x)=√{square root over (x)}    -   Swap(x,y)=(y, x)    -   Tan(x) the trigonometric tangent function operating on an        argument x in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   -   Operations of a higher precedence are evaluated before any        operation of a lower precedence.    -   Operations of the same precedence are evaluated sequentially        from left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table) operations (with operands x, y, and z)   “x++”, “x− −”“!x”, “−x” (as a unary prefix operator) x^(y)${``{x*y}"},{``{x/y}"},{``{x \div y}"},{``\frac{x}{y}"},{``{x\mspace{14mu}\%\mspace{14mu} y}"}$${``{x + y}"},{{``{x - y}"}\mspace{14mu}\left( {{as}\mspace{14mu} a\mspace{14mu}{two}\text{-}{arguement}\mspace{14mu}{operator}} \right)},{``{\sum\limits_{i = x}^{y}{f(i)}}"}$“x << y”, “x >> y” “x < y”, “x <= y”, “x > y”, “x >= y” “x = = y”, “x !=y” “x & y” “x | y” “x && y” “x | | y” “x ? y : z” “x . . . y” “x = y”,“x += y”, “x −= y”

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 else if( condition 1 )  statement 1 ...else /* informative remark on remaining condition */  statement n

-   -   may be described in the following manner:    -   . . . as follows / . . . the following applies:        -   If condition 0, statement 0        -   Otherwise, if condition 1, statement 1        -   . . .        -   Otherwise (informative remark on remaining condition),            statement n

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in thetext is introduced with “ . . . as follows” or “ . . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . “statements can be identified by matching” . . . asfollows” or “ . . . the following applies” with the ending “Otherwise .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

  if( condition 0a && condition 0b )  statement 0 else if( condition1a ∥ condition 1b )  statement 1 ... else  statement n

-   -   may be described in the following manner:    -   . . . as follows / . . . the following applies:        -   If all of the following conditions are true, statement 0:            -   condition 0a            -   condition 0b        -   Otherwise, if one or more of the following conditions are            true, statement 1:            -   condition 1a            -   condition 1b        -   . . .        -   Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

-   -   if(condition 0)        -   statement 0    -   if(condition 1)        -   statement 1

may be described in the following manner:

-   -   When condition 0, statement 0    -   When condition 1, statement 1.

Although embodiments of the disclosure have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g. with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

What is claimed is:
 1. A method of decoding a video bitstreamimplemented by a decoding device, the method comprising: obtaining avalue of a first syntax element from a sequence parameter set (SPS),wherein the value of the first syntax element is used to specify whethera decoded picture buffer (DPB) parameters syntax structure is present inthe SPS, wherein the SPS is coded in the video bitstream and containssyntax elements that apply to a video sequence; and obtaining a value ofa second syntax element from the SPS, at least when determining that thevalue of the first syntax element specifies that the DPB parameterssyntax structure is present in the SPS, wherein the value of the secondsyntax element is used to specify presence of a DPB syntax element inthe DPB parameters syntax structure, wherein the DPB syntax element isapplied to a temporal sublayer except for a highest temporal sublayer inthe video sequence.
 2. The method of claim 1, further comprising:obtaining a value of the DPB syntax element based on the value of thesecond syntax element; and reconstructing the video sequence based onthe value of the DPB syntax element.
 3. The method of claim 2, whereinthe obtaining the value of the DPB syntax element based on the value ofthe second syntax element comprises: obtaining the value of the DPBsyntax element from the DPB parameters syntax structure, whendetermining that the value of the second syntax element specifies thatthe DPB syntax element is present in the DPB parameters syntaxstructure; or setting the value of the DPB syntax element equal to avalue of another DPB syntax element applied to the highest temporalsublayer in the DPB parameters syntax structure, when determining thatthe value of the second syntax element specifies that the DPB syntaxelement is not present in the DPB parameters syntax structure.
 4. Themethod of claim 2, wherein the reconstructing the video sequence basedon the value of the DPB syntax element comprises: configuring the DPBbased on the value of the DPB syntax element; and reconstructing thevideo sequence using the DPB.
 5. The method of claim 2, wherein thereconstructing the video sequence based on the value of the DPB syntaxelement comprises: reconstructing the video sequence based ondetermining that the DPB used satisfies a requirement specified by thevalue of the DPB syntax element.
 6. The method of claim 1, furthercomprising: obtaining a value of a third syntax element from the SPS,wherein the value of the third syntax element is used to determine amaximum number of temporal sublayers that are present in the videosequence.
 7. The method of claim 6, wherein the obtaining the value ofthe second syntax element from the SPS comprises: determining whetherthe maximum number of the temporal sublayers in the video bitstream isgreater than 1 based on the value of the third syntax element, whendetermining that the value of the first syntax element specifies thatthe DPB parameters syntax structure is present in the SPS; and obtainingthe value of the second syntax element from the SPS, when determiningthat the maximum number of the temporal sublayers is greater than one.8. A method of encoding a video bitstream implemented by an encodingdevice, the method comprising: determining presence of a decoded picturebuffer (DPB) parameters syntax structure in a sequence parameter set(SPS), wherein the SPS is encoded in the video bitstream and containssyntax elements that apply to a video sequence; encoding a value of afirst syntax element into the SPS based on the determining of thepresence of the DPB parameters syntax structure in the SPS, wherein thevalue of the first syntax element is used to specify whether the DPBparameters syntax structure is present in the SPS; determining presenceof a DPB syntax element in the DPB parameters syntax structure, whendetermining that the DPB parameters syntax structure is present in theSPS, wherein the DPB syntax element is applied to a temporal sublayerexcept for a highest temporal sublayer in the video sequence; andencoding a value of a second syntax element into the SPS based on thedetermining of the presence of the DPB syntax element in the DPBparameters syntax structure, wherein the value of the second syntaxelement is used to specify the presence of the DPB syntax element in theDPB parameters syntax structure.
 9. The method of claim 8, furthercomprising: determining a value of the DPB syntax element whendetermining that the DPB syntax element is present in the DPB parameterssyntax structure; and reconstructing the video sequence based on thevalue of the DPB syntax element.
 10. The method of claim 8, furthercomprising: setting the value of the DPB syntax element equal to a valueof another DPB syntax element applied to the highest temporal sublayerin the DPB parameters syntax structure; and reconstructing the videosequence based on the value of the DPB syntax element.
 11. The method ofclaim 9, wherein the reconstructing the video sequence based on thevalue of the DPB syntax element comprises: configuring the DPB tosatisfy the value of the DPB syntax element; and reconstructing thevideo sequence using the DPB.
 12. The method of claim 8, wherein thepresence of a DPB syntax element in the DPB parameters syntax structureis determined, when it is determined that the DPB parameters syntaxstructure is present in the SPS and a maximum number of temporalsublayers in the video bitstream is greater than one.
 13. An apparatusfor decoding a coded video bitstream, wherein the apparatus comprises:an obtaining unit configured to obtain a value of a first syntax elementfrom a sequence parameter set (SPS) coded in the video bitstream,wherein the value of the first syntax element is used to specify whethera decoded picture buffer (DPB) parameters syntax structure is present inthe SPS; and a determining unit configured to determine whether thevalue of the first syntax element specifies that the DPB parameterssyntax structure is present in the SPS; and wherein the obtaining unitis further configured to obtain a value of a second syntax element fromthe SPS, at least when determining that the value of the first syntaxelement specifies that the DPB parameters syntax structure is present inthe SPS, wherein the value of the second syntax element is used tospecify presence of a DPB syntax element in the DPB parameters syntaxstructure, wherein the DPB syntax element is applied to a temporalsublayer except for a highest temporal sublayer in a video sequence. 14.An apparatus for encoding a video bitstream, wherein the apparatuscomprises: a determining unit configured to determine presence of adecoded picture buffer (DPB) parameters syntax structure in a sequenceparameter set (SPS) encoded in the video bitstream; and an encoding unitconfigured to encode a value of a first syntax element into the SPSbased on the determining of the presence of the DPB parameters syntaxstructure in the SPS, wherein the value of the first syntax element isused to specify whether the DPB parameters syntax structure is presentin the SPS; wherein the determining unit is further configured todetermine presence of a DPB syntax element in the DPB parameters syntaxstructure, when determining that the DPB parameters syntax structure ispresent in the SPS, wherein the DPB syntax element is applied to atemporal sublayer except for a highest temporal sublayer in a videosequence; and wherein the encoding unit is further configured to encodea value of a second syntax element into the SPS based on the determiningof the presence of the DPB syntax element in the DPB parameters syntaxstructure, wherein the value of the second syntax element is used tospecify the presence of the DPB syntax element in the DPB parameterssyntax structure.
 15. A computer program product embodied on anon-transitory computer-readable medium, the computer program productcomprising a program code for performing the method according to claim 1when executed on a computer or a processor.
 16. A decoder, comprising:one or more processors; and a non-transitory computer-readable storagemedium coupled to the processors and storing programming for executionby the processors, wherein the programming, when executed by theprocessors, configures the decoder to carry out the method according toclaim
 1. 17. An encoder, comprising: one or more processors; and anon-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures theencoder to carry out the method according to claim
 8. 18. Anon-transitory computer-readable medium carrying a program code which,when executed by a computer device, causes the computer device toperform the method of claim
 1. 19. A non-transitory storage medium whichincludes an encoded bitstream, the bitstream being generated by dividinga current picture of a video signal or an image signal into a pluralityblocks, and comprising a plurality of syntax elements, wherein theplurality of syntax elements comprises a first syntax element in asequence parameter set (SPS), wherein the value of the first syntaxelement is used to specify whether a decoded picture buffer (DPB)parameters syntax structure is present in the SPS; in case that thevalue of the first syntax element specifies that the DPB parameterssyntax structure is present in the SPS, the bitstream further comprisesa second syntax element in the SPS, wherein the value of the secondsyntax element is used to specify presence of a DPB syntax element inthe DPB parameters syntax structure, wherein the DPB syntax element isapplied to a temporal sublayer except for a highest temporal sublayer ina video sequence.